Unlicensed Cell Downlink Signal Synchronization

ABSTRACT

A wireless device receives at least one control message comprising configuration parameters of a first unlicensed cell and a second unlicensed cell. The wireless device receives, via the first unlicensed cell, a first signal comprising a first downlink synchronization signal. The wireless device receives, via the second unlicensed cell, a second signal comprising a second downlink synchronization signal. The wireless device synchronizes a first downlink signal timing with the first unlicensed cell based on the second signal received via the second unlicensed cell. The wireless device synchronizes a second downlink signal timing with the second unlicensed cell based on the first signal received via the first unlicensed cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/263,440, filed Sep. 13, 2016, which claims the benefit of U.S.Provisional Application No. 62/218,467, filed Sep. 14, 2015, all ofwhich are hereby incorporated by reference in their entireties.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Examples of several of the various embodiments of the present inventionare described herein with reference to the drawings.

FIG. 1 is a diagram depicting example sets of OFDM subcarriers as per anaspect of an embodiment of the present invention.

FIG. 2 is a diagram depicting an example transmission time and receptiontime for two carriers in a carrier group as per an aspect of anembodiment of the present invention.

FIG. 3 is a diagram depicting OFDM radio resources as per an aspect ofan embodiment of the present invention.

FIG. 4 is a block diagram of a base station and a wireless device as peran aspect of an embodiment of the present invention.

FIG. 5A, FIG. 5B, FIG. 5C and FIG. 5D are example diagrams for uplinkand downlink signal transmission as per an aspect of an embodiment ofthe present invention.

FIG. 6 is an example diagram for a protocol structure with CA and DC asper an aspect of an embodiment of the present invention.

FIG. 7 is an example diagram for a protocol structure with CA and DC asper an aspect of an embodiment of the present invention.

FIG. 8 shows example TAG configurations as per an aspect of anembodiment of the present invention.

FIG. 9 is an example message flow in a random access process in asecondary TAG as per an aspect of an embodiment of the presentinvention.

FIG. 10 is an example diagram depicting downlink reception timing of oneor more cells in TAG1 and TAG2 as per an aspect of an embodiment of thepresent invention.

FIG. 11 is an example diagram depicting signal timing of one or morecells as per an aspect of an embodiment of the present invention.

FIG. 12 is an example diagram depicting signal timing of one or morecells as per an aspect of an embodiment of the present invention.

FIG. 13 is an example diagram depicting signal timing of one or morecells as per an aspect of an embodiment of the present invention.

FIG. 14 is an example diagram depicting signal timing of one or morecells as per an aspect of an embodiment of the present invention.

FIG. 15 is an example flow diagram as per an aspect of an embodiment ofthe present invention.

FIG. 16 is an example flow diagram as per an aspect of an embodiment ofthe present invention.

FIG. 17 is an example flow diagram as per an aspect of an embodiment ofthe present invention.

FIG. 18 is an example flow diagram as per an aspect of an embodiment ofthe present invention.

FIG. 19 is an example flow diagram as per an aspect of an embodiment ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Example embodiments of the present invention enable operation of carrieraggregation. Embodiments of the technology disclosed herein may beemployed in the technical field of multicarrier communication systems.More particularly, the embodiments of the technology disclosed hereinmay relate to signal timing in a multicarrier communication system.

The following Acronyms are used throughout the present disclosure:

ASIC application-specific integrated circuit

BPSK binary phase shift keying

CA carrier aggregation

CSI channel state information

CDMA code division multiple access

CSS common search space

CPLD complex programmable logic devices

CC component carrier

DL downlink

DCI downlink control information

DC dual connectivity

EPC evolved packet core

E-UTRAN evolved-universal terrestrial radio access network

FPGA field programmable gate arrays

FDD frequency division multiplexing

HDL hardware description languages

HARQ hybrid automatic repeat request

IE information element

LTE long term evolution

MCG master cell group

MeNB master evolved node B

MIB master information block

MAC media access control

MAC media access control

MME mobility management entity

NAS non-access stratum

OFDM orthogonal frequency division multiplexing

PDCP packet data convergence protocol

PDU packet data unit

PHY physical

PDCCH physical downlink control channel

PHICH physical HARQ indicator channel

PUCCH physical uplink control channel

PUSCH physical uplink shared channel

PCell primary cell

PCell primary cell

PCC primary component carrier

PSCell primary secondary cell

pTAG primary timing advance group

QAM quadrature amplitude modulation

QPSK quadrature phase shift keying

RBG Resource Block Groups

RLC radio link control

RRC radio resource control

RA random access

RB resource blocks

SCC secondary component carrier

SCell secondary cell

Scell secondary cells

SCG secondary cell group

SeNB secondary evolved node B

sTAGs secondary timing advance group

SDU service data unit

S-GW serving gateway

SRB signaling radio bearer

SC-OFDM single carrier-OFDM

SFN system frame number

SIB system information block

TAI tracking area identifier

TAT time alignment timer

TDD time division duplexing

TDMA time division multiple access

TA timing advance

TAG timing advance group

TB transport block

UL uplink

UE user equipment

VHDL VHSIC hardware description language

Example embodiments of the invention may be implemented using variousphysical layer modulation and transmission mechanisms. Exampletransmission mechanisms may include, but are not limited to: CDMA, OFDM,TDMA, Wavelet technologies, and/or the like. Hybrid transmissionmechanisms such as TDMA/CDMA, and OFDM/CDMA may also be employed.Various modulation schemes may be applied for signal transmission in thephysical layer. Examples of modulation schemes include, but are notlimited to: phase, amplitude, code, a combination of these, and/or thelike. An example radio transmission method may implement QAM using BPSK,QPSK, 16-QAM, 64-QAM, 256-QAM, and/or the like. Physical radiotransmission may be enhanced by dynamically or semi-dynamically changingthe modulation and coding scheme depending on transmission requirementsand radio conditions.

FIG. 1 is a diagram depicting example sets of OFDM subcarriers as per anaspect of an embodiment of the present invention. As illustrated in thisexample, arrow(s) in the diagram may depict a subcarrier in amulticarrier OFDM system. The OFDM system may use technology such asOFDM technology, DFTS-OFDM, SC-OFDM technology, or the like. Forexample, arrow 101 shows a subcarrier transmitting information symbols.FIG. 1 is for illustration purposes, and a typical multicarrier OFDMsystem may include more subcarriers in a carrier. For example, thenumber of subcarriers in a carrier may be in the range of 10 to 10,000subcarriers. FIG. 1 shows two guard bands 106 and 107 in a transmissionband. As illustrated in FIG. 1, guard band 106 is between subcarriers103 and subcarriers 104. The example set of subcarriers A 102 includessubcarriers 103 and subcarriers 104. FIG. 1 also illustrates an exampleset of subcarriers B 105. As illustrated, there is no guard band betweenany two subcarriers in the example set of subcarriers B 105. Carriers ina multicarrier OFDM communication system may be contiguous carriers,non-contiguous carriers, or a combination of both contiguous andnon-contiguous carriers.

FIG. 2 is a diagram depicting an example transmission time and receptiontime for two carriers as per an aspect of an embodiment of the presentinvention. A multicarrier OFDM communication system may include one ormore carriers, for example, ranging from 1 to 10 carriers. Carrier A 204and carrier B 205 may have the same or different timing structures.Although FIG. 2 shows two synchronized carriers, carrier A 204 andcarrier B 205 may or may not be synchronized with each other. Differentradio frame structures may be supported for FDD and TDD duplexmechanisms. FIG. 2 shows an example FDD frame timing. Downlink anduplink transmissions may be organized into radio frames 201. In thisexample, radio frame duration is 10 msec. Other frame durations, forexample, in the range of 1 to 100 msec may also be supported. In thisexample, each 10 msec radio frame 201 may be divided into ten equallysized subframes 202. Other subframe durations such as including 0.5msec, 1 msec, 2 msec, and 5 msec may also be supported. Subframe(s) mayconsist of two or more slots (e.g. slots 206 and 207). For the exampleof FDD, 10 subframes may be available for downlink transmission and 10subframes may be available for uplink transmissions in each 10 msecinterval. Uplink and downlink transmissions may be separated in thefrequency domain. Slot(s) may include a plurality of OFDM symbols 203.The number of OFDM symbols 203 in a slot 206 may depend on the cyclicprefix length and subcarrier spacing.

FIG. 3 is a diagram depicting OFDM radio resources as per an aspect ofan embodiment of the present invention. The resource grid structure intime 304 and frequency 305 is illustrated in FIG. 3. The quantity ofdownlink subcarriers or RBs (in this example 6 to 100 RBs) may depend,at least in part, on the downlink transmission bandwidth 306 configuredin the cell. The smallest radio resource unit may be called a resourceelement (e.g. 301). Resource elements may be grouped into resourceblocks (e.g. 302). Resource blocks may be grouped into larger radioresources called Resource Block Groups (RBG) (e.g. 303). The transmittedsignal in slot 206 may be described by one or several resource grids ofa plurality of subcarriers and a plurality of OFDM symbols. Resourceblocks may be used to describe the mapping of certain physical channelsto resource elements. Other pre-defined groupings of physical resourceelements may be implemented in the system depending on the radiotechnology. For example, 24 subcarriers may be grouped as a radio blockfor a duration of 5 msec. In an illustrative example, a resource blockmay correspond to one slot in the time domain and 180 kHz in thefrequency domain (for 15 KHz subcarrier bandwidth and 12 subcarriers).

FIG. 5A, FIG. 5B, FIG. 5C and FIG. 5D are example diagrams for uplinkand downlink signal transmission as per an aspect of an embodiment ofthe present invention. FIG. 5A shows an example uplink physical channel.The baseband signal representing the physical uplink shared channel mayperform the following processes. These functions are illustrated asexamples and it is anticipated that other mechanisms may be implementedin various embodiments. The functions may comprise scrambling,modulation of scrambled bits to generate complex-valued symbols, mappingof the complex-valued modulation symbols onto one or severaltransmission layers, transform precoding to generate complex-valuedsymbols, precoding of the complex-valued symbols, mapping of precodedcomplex-valued symbols to resource elements, generation ofcomplex-valued time-domain DFTS-OFDM/SC-FDMA signal for each antennaport, and/or the like.

Example modulation and up-conversion to the carrier frequency of thecomplex-valued DFTS-OFDM/SC-FDMA baseband signal for each antenna portand/or the complex-valued PRACH baseband signal is shown in FIG. 5B.Filtering may be employed prior to transmission.

An example structure for Downlink Transmissions is shown in FIG. 5C. Thebaseband signal representing a downlink physical channel may perform thefollowing processes. These functions are illustrated as examples and itis anticipated that other mechanisms may be implemented in variousembodiments. The functions include scrambling of coded bits in each ofthe codewords to be transmitted on a physical channel; modulation ofscrambled bits to generate complex-valued modulation symbols; mapping ofthe complex-valued modulation symbols onto one or several transmissionlayers; precoding of the complex-valued modulation symbols on each layerfor transmission on the antenna ports; mapping of complex-valuedmodulation symbols for each antenna port to resource elements;generation of complex-valued time-domain OFDM signal for each antennaport, and/or the like.

Example modulation and up-conversion to the carrier frequency of thecomplex-valued OFDM baseband signal for each antenna port is shown inFIG. 5D. Filtering may be employed prior to transmission.

FIG. 4 is an example block diagram of a base station 401 and a wirelessdevice 406, as per an aspect of an embodiment of the present invention.A communication network 400 may include at least one base station 401and at least one wireless device 406. The base station 401 may includeat least one communication interface 402, at least one processor 403,and at least one set of program code instructions 405 stored innon-transitory memory 404 and executable by the at least one processor403. The wireless device 406 may include at least one communicationinterface 407, at least one processor 408, and at least one set ofprogram code instructions 410 stored in non-transitory memory 409 andexecutable by the at least one processor 408. Communication interface402 in base station 401 may be configured to engage in communicationwith communication interface 407 in wireless device 406 via acommunication path that includes at least one wireless link 411.Wireless link 411 may be a bi-directional link. Communication interface407 in wireless device 406 may also be configured to engage in acommunication with communication interface 402 in base station 401. Basestation 401 and wireless device 406 may be configured to send andreceive data over wireless link 411 using multiple frequency carriers.According to some of the various aspects of embodiments, transceiver(s)may be employed. A transceiver is a device that includes bothtransmitter and receiver circuitry. Transceivers may be employed indevices such as wireless devices, base stations, relay nodes, and/or thelike. Example embodiments for radio technology implemented incommunication interface 402, 407 and wireless link 411 are illustratedare FIG. 1, FIG. 2, FIG. 3, FIG. 5, and associated text.

An interface may be a hardware interface, a firmware interface, asoftware interface, and/or a combination thereof. The hardware interfacemay include connectors, wires, electronic devices such as drivers,amplifiers, and/or the like. A software interface may include codestored in a memory device to implement protocol(s), protocol layers,communication drivers, device drivers, combinations thereof, and/or thelike. A firmware interface may include a combination of embeddedhardware and code stored in and/or in communication with a memory deviceto implement connections, electronic device operations, protocol(s),protocol layers, communication drivers, device drivers, hardwareoperations, combinations thereof, and/or the like.

The term configured may relate to the capacity of a device whether thedevice is in an operational or non-operational state. Configured mayalso refer to specific settings in a device that effect the operationalcharacteristics of the device whether the device is in an operational ornon-operational state. In other words, the hardware, software, firmware,registers, memory values, and/or the like may be “configured” within adevice, whether the device is in an operational or nonoperational state,to provide the device with specific characteristics. Terms such as “acontrol message to cause in a device” may mean that a control messagehas parameters that may be used to configure specific characteristics inthe device, whether the device is in an operational or non-operationalstate.

According to some of the various aspects of embodiments, an LTE networkmay include a multitude of base stations, providing a user planePDCP/RLC/MAC/PHY and control plane (RRC) protocol terminations towardsthe wireless device. The base station(s) may be interconnected withother base station(s) (e.g. employing an X2 interface). The basestations may also be connected employing, for example, an S1 interfaceto an EPC. For example, the base stations may be interconnected to theMME employing the S1-MME interface and to the S-G) employing the S1-Uinterface. The S1 interface may support a many-to-many relation betweenMMEs/Serving Gateways and base stations. A base station may include manysectors for example: 1, 2, 3, 4, or 6 sectors. A base station mayinclude many cells, for example, ranging from 1 to 50 cells or more. Acell may be categorized, for example, as a primary cell or secondarycell. At RRC connection establishment/re-establishment/handover, oneserving cell may provide the NAS (non-access stratum) mobilityinformation (e.g. TAI), and at RRC connection re-establishment/handover,one serving cell may provide the security input. This cell may bereferred to as the Primary Cell (PCell). In the downlink, the carriercorresponding to the PCell may be the Downlink Primary Component Carrier(DL PCC), while in the uplink, it may be the Uplink Primary ComponentCarrier (UL PCC). Depending on wireless device capabilities, SecondaryCells (SCells) may be configured to form together with the PCell a setof serving cells. In the downlink, the carrier corresponding to an SCellmay be a Downlink Secondary Component Carrier (DL SCC), while in theuplink, it may be an Uplink Secondary Component Carrier (UL SCC). AnSCell may or may not have an uplink carrier.

A cell, comprising a downlink carrier and optionally an uplink carrier,may be assigned a physical cell ID and a cell index. A carrier (downlinkor uplink) may belong to only one cell. The cell ID or Cell index mayalso identify the downlink carrier or uplink carrier of the cell(depending on the context it is used). In the specification, cell ID maybe equally referred to a carrier ID, and cell index may be referred tocarrier index. In implementation, the physical cell ID or cell index maybe assigned to a cell. A cell ID may be determined using asynchronization signal transmitted on a downlink carrier. A cell indexmay be determined using RRC messages. For example, when thespecification refers to a first physical cell ID for a first downlinkcarrier, the specification may mean the first physical cell ID is for acell comprising the first downlink carrier. The same concept may applyto, for example, carrier activation. When the specification indicatesthat a first carrier is activated, the specification may equally meanthat the cell comprising the first carrier is activated.

Embodiments may be configured to operate as needed. The disclosedmechanism may be performed when certain criteria are met, for example,in a wireless device, a base station, a radio environment, a network, acombination of the above, and/or the like. Example criteria may bebased, at least in part, on for example, traffic load, initial systemset up, packet sizes, traffic characteristics, a combination of theabove, and/or the like. When the one or more criteria are met, variousexample embodiments may be applied. Therefore, it may be possible toimplement example embodiments that selectively implement disclosedprotocols.

A base station may communicate with a mix of wireless devices. Wirelessdevices may support multiple technologies, and/or multiple releases ofthe same technology. Wireless devices may have some specificcapability(ies) depending on its wireless device category and/orcapability(ies). A base station may comprise multiple sectors. When thisdisclosure refers to a base station communicating with a plurality ofwireless devices, this disclosure may refer to a subset of the totalwireless devices in a coverage area. This disclosure may refer to, forexample, a plurality of wireless devices of a given LTE release with agiven capability and in a given sector of the base station. Theplurality of wireless devices in this disclosure may refer to a selectedplurality of wireless devices, and/or a subset of total wireless devicesin a coverage area which perform according to disclosed methods, and/orthe like. There may be a plurality of wireless devices in a coveragearea that may not comply with the disclosed methods, for example,because those wireless devices perform based on older releases of LTEtechnology.

FIG. 6 and FIG. 7 are example diagrams for protocol structure with CAand DC as per an aspect of an embodiment of the present invention.E-UTRAN may support Dual Connectivity (DC) operation whereby a multipleRX/TX UE in RRC_CONNECTED may be configured to utilize radio resourcesprovided by two schedulers located in two eNBs connected via a non-idealbackhaul over the X2 interface. eNBs involved in DC for a certain UE mayassume two different roles: an eNB may either act as an MeNB or as anSeNB. In DC, a UE may be connected to one MeNB and one SeNB. Mechanismsimplemented in DC may be extended to cover more than two eNBs. FIG. 7illustrates one example structure for the UE side MAC entities when aMaster Cell Group (MCG) and a Secondary Cell Group (SCG) are configured,and it may not restrict implementation. Media Broadcast MulticastService (MBMS) reception is not shown in this figure for simplicity.

In DC, the radio protocol architecture that a particular bearer uses maydepend on how the bearer is setup. Three alternatives may exist, an MCGbearer, an SCG bearer and a split bearer as shown in FIG. 6. RRC may belocated in MeNB and SRBs may be configured as a MCG bearer type and mayuse the radio resources of the MeNB. DC may also be described as havingat least one bearer configured to use radio resources provided by theSeNB. DC may or may not be configured/implemented in example embodimentsof the invention.

In the case of DC, the UE may be configured with two MAC entities: oneMAC entity for MeNB, and one MAC entity for SeNB. In DC, the configuredset of serving cells for a UE may comprise two subsets: a Master CellGroup (MCG) containing the serving cells of the MeNB, and the SecondaryCell Group (SCG) containing the serving cells of the SeNB. For a SCG,one or more of the following may be applied: at least one cell in theSCG has a configured UL CC and one of them, named PSCell (or PCell ofSCG, or sometimes called PCell), is configured with PUCCH resources;when the SCG is configured, there may be at least one SCG bearer or oneSplit bearer; upon detection of a physical layer problem or a randomaccess problem on a PSCell, or the maximum number of RLC retransmissionshas been reached associated with the SCG, or upon detection of an accessproblem on a PSCell during a SCG addition or a SCG change: a RRCconnection re-establishment procedure may not be triggered, ULtransmissions towards cells of the SCG are stopped, a MeNB may beinformed by the UE of a SCG failure type, for split bearer, the DL datatransfer over the MeNB is maintained; the RLC AM bearer may beconfigured for the split bearer; like PCell, PSCell may not bede-activated; PSCell may be changed with a SCG change (e.g. withsecurity key change and a RACH procedure); and/or neither a directbearer type change between a Split bearer and a SCG bearer norsimultaneous configuration of a SCG and a Split bearer are supported.

With respect to the interaction between a MeNB and a SeNB, one or moreof the following principles may be applied: the MeNB may maintain theRRM measurement configuration of the UE and may, (e.g., based onreceived measurement reports or traffic conditions or bearer types),decide to ask a SeNB to provide additional resources (serving cells) fora UE; upon receiving a request from the MeNB, a SeNB may create acontainer that may result in the configuration of additional servingcells for the UE (or decide that it has no resource available to do so);for UE capability coordination, the MeNB may provide (part of) the ASconfiguration and the UE capabilities to the SeNB; the MeNB and the SeNBmay exchange information about a UE configuration by employing of RRCcontainers (inter-node messages) carried in X2 messages; the SeNB mayinitiate a reconfiguration of its existing serving cells (e.g., PUCCHtowards the SeNB); the SeNB may decide which cell is the PSCell withinthe SCG; the MeNB may not change the content of the RRC configurationprovided by the SeNB; in the case of a SCG addition and a SCG SCelladdition, the MeNB may provide the latest measurement results for theSCG cell(s); both a MeNB and a SeNB may know the SFN and subframe offsetof each other by OAM, (e.g., for the purpose of DRX alignment andidentification of a measurement gap). In an example, when adding a newSCG SCell, dedicated RRC signalling may be used for sending requiredsystem information of the cell as for CA, except for the SFN acquiredfrom a MIB of the PSCell of a SCG.

In an example, serving cells may be grouped in a TA group (TAG). Servingcells in one TAG may use the same timing reference. For a given TAG,user equipment (UE) may use at least one downlink carrier as a timingreference. For a given TAG, a UE may synchronize uplink subframe andframe transmission timing of uplink carriers belonging to the same TAG.In an example, serving cells having an uplink to which the same TAapplies may correspond to serving cells hosted by the same receiver. AUE supporting multiple TAs may support two or more TA groups. One TAgroup may contain the PCell and may be called a primary TAG (pTAG). In amultiple TAG configuration, at least one TA group may not contain thePCell and may be called a secondary TAG (sTAG). In an example, carrierswithin the same TA group may use the same TA value and/or the sametiming reference. When DC is configured, cells belonging to a cell group(MCG or SCG) may be grouped into multiple TAGs including a pTAG and oneor more sTAGs.

FIG. 8 shows example TAG configurations as per an aspect of anembodiment of the present invention. In Example 1, pTAG comprises PCell,and an sTAG comprises SCell1. In Example 2, a pTAG comprises a PCell andSCell1, and an sTAG comprises SCell2 and SCell3. In Example 3, pTAGcomprises PCell and SCell1, and an sTAG1 includes SCell2 and SCell3, andsTAG2 comprises SCell4. Up to four TAGs may be supported in a cell group(MCG or SCG) and other example TAG configurations may also be provided.In various examples in this disclosure, example mechanisms are describedfor a pTAG and an sTAG. Some of the example mechanisms may be applied toconfigurations with multiple sTAGs.

In an example, an eNB may initiate an RA procedure via a PDCCH order foran activated SCell. This PDCCH order may be sent on a scheduling cell ofthis SCell. When cross carrier scheduling is configured for a cell, thescheduling cell may be different than the cell that is employed forpreamble transmission, and the PDCCH order may include an SCell index.At least a non-contention based RA procedure may be supported forSCell(s) assigned to sTAG(s).

FIG. 9 is an example message flow in a random access process in asecondary TAG as per an aspect of an embodiment of the presentinvention. An eNB transmits an activation command 600 to activate anSCell. A preamble 602 (Msg1) may be sent by a UE in response to a PDCCHorder 601 on an SCell belonging to an sTAG. In an example embodiment,preamble transmission for SCells may be controlled by the network usingPDCCH format 1A. Msg2 message 603 (RAR: random access response) inresponse to the preamble transmission on the SCell may be addressed toRA-RNTI in a PCell common search space (CSS). Uplink packets 604 may betransmitted on the SCell in which the preamble was transmitted.

According to some of the various aspects of embodiments, initial timingalignment may be achieved through a random access procedure. This mayinvolve a UE transmitting a random access preamble and an eNB respondingwith an initial TA command NTA (amount of timing advance) within arandom access response window. The start of the random access preamblemay be aligned with the start of a corresponding uplink subframe at theUE assuming NTA=0. The eNB may estimate the uplink timing from therandom access preamble transmitted by the UE. The TA command may bederived by the eNB based on the estimation of the difference between thedesired UL timing and the actual UL timing. The UE may determine theinitial uplink transmission timing relative to the correspondingdownlink of the sTAG on which the preamble is transmitted.

The mapping of a serving cell to a TAG may be configured by a servingeNB with RRC signaling. The mechanism for TAG configuration andreconfiguration may be based on RRC signaling. According to some of thevarious aspects of embodiments, when an eNB performs an SCell additionconfiguration, the related TAG configuration may be configured for theSCell. In an example embodiment, an eNB may modify the TAG configurationof an SCell by removing (releasing) the SCell and adding(configuring) anew SCell (with the same physical cell ID and frequency) with an updatedTAG ID. The new SCell with the updated TAG ID may initially be inactivesubsequent to being assigned the updated TAG ID. The eNB may activatethe updated new SCell and start scheduling packets on the activatedSCell. In an example implementation, it may not be possible to changethe TAG associated with an SCell, but rather, the SCell may need to beremoved and a new SCell may need to be added with another TAG. Forexample, if there is a need to move an SCell from an sTAG to a pTAG, atleast one RRC message, for example, at least one RRC reconfigurationmessage, may be send to the UE to reconfigure TAG configurations byreleasing the SCell and then configuring the SCell as a part of the pTAG(when an SCell is added/configured without a TAG index, the SCell may beexplicitly assigned to the pTAG). The PCell may not change its TA groupand may be a member of the pTAG.

The purpose of an RRC connection reconfiguration procedure may be tomodify an RRC connection, (e.g. to establish, modify and/or release RBs,to perform handover, to setup, modify, and/or release measurements, toadd, modify, and/or release SCells). If the received RRC ConnectionReconfiguration message includes the sCellToReleaseList, the UE mayperform an SCell release. If the received RRC Connection Reconfigurationmessage includes the sCellToAddModList, the UE may perform SCelladditions or modification.

In LTE Release-10 and Release-11 CA, a PUCCH is only transmitted on thePCell (PSCell) to an eNB. In LTE-Release 12 and earlier, a UE maytransmit PUCCH information on one cell (PCell or PSCell) to a given eNB.

As the number of CA capable UEs and also the number of aggregatedcarriers increase, the number of PUCCHs and also the PUCCH payload sizemay increase. Accommodating the PUCCH transmissions on the PCell maylead to a high PUCCH load on the PCell. A PUCCH on an SCell may beintroduced to offload the PUCCH resource from the PCell. More than onePUCCH may be configured for example, a PUCCH on a PCell and anotherPUCCH on an SCell. In the example embodiments, one, two or more cellsmay be configured with PUCCH resources for transmitting CSI/ACK/NACK toa base station. Cells may be grouped into multiple PUCCH groups, and oneor more cell within a group may be configured with a PUCCH. In anexample configuration, one SCell may belong to one PUCCH group. SCellswith a configured PUCCH transmitted to a base station may be called aPUCCH SCell, and a cell group with a common PUCCH resource transmittedto the same base station may be called a PUCCH group.

In an example embodiment, a MAC entity may have a configurable timertimeAlignmentTimer per TAG. The timeAlignmentTimer may be used tocontrol how long the MAC entity considers the Serving Cells belonging tothe associated TAG to be uplink time aligned. The MAC entity may, when aTiming Advance Command MAC control element is received, apply the TimingAdvance Command for the indicated TAG; start or restart thetimeAlignmentTimer associated with the indicated TAG. The MAC entitymay, when a Timing Advance Command is received in a Random AccessResponse message for a serving cell belonging to a TAG and/or if theRandom Access Preamble was not selected by the MAC entity, apply theTiming Advance Command for this TAG and start or restart thetimeAlignmentTimer associated with this TAG. Otherwise, if thetimeAlignmentTimer associated with this TAG is not running, the TimingAdvance Command for this TAG may be applied and the timeAlignmentTimerassociated with this TAG started. When the contention resolution isconsidered not successful, a timeAlignmentTimer associated with this TAGmay be stopped. Otherwise, the MAC entity may ignore the received TimingAdvance Command.

In example embodiments, a timer is running once it is started, until itis stopped or until it expires; otherwise it may not be running. A timercan be started if it is not running or restarted if it is running. Forexample, a timer may be started or restarted from its initial value.

Example embodiments of the invention may enable operation ofmulti-carrier communications. Other example embodiments may comprise anon-transitory tangible computer readable media comprising instructionsexecutable by one or more processors to cause operation of multi-carriercommunications. Yet other example embodiments may comprise an article ofmanufacture that comprises a non-transitory tangible computer readablemachine-accessible medium having instructions encoded thereon forenabling programmable hardware to cause a device (e.g. wirelesscommunicator, UE, base station, etc.) to enable operation ofmulti-carrier communications. The device may include processors, memory,interfaces, and/or the like. Other example embodiments may comprisecommunication networks comprising devices such as base stations,wireless devices (or user equipment: UE), servers, switches, antennas,and/or the like.

The amount of data traffic carried over cellular networks is expected toincrease for many years to come. The number of users/devices isincreasing and each user/device accesses an increasing number andvariety of services, e.g. video delivery, large files, images. Thisrequires not only high capacity in the network, but also provisioningvery high data rates to meet customers' expectations on interactivityand responsiveness. More spectrum is therefore needed for cellularoperators to meet the increasing demand. Considering user expectationsof high data rates along with seamless mobility, it may be beneficialthat more spectrum be made available for deploying macro cells as wellas small cells for cellular systems.

Striving to meet the market demands, there has been increasing interestfrom operators in deploying some complementary access utilizingunlicensed spectrum to meet the traffic growth. This is exemplified bythe large number of operator-deployed Wi-Fi networks and the 3GPPstandardization of LTE/WLAN interworking solutions. This interestindicates that unlicensed spectrum, when present, may be an effectivecomplement to licensed spectrum for cellular operators to helpaddressing the traffic explosion in some scenarios, such as hotspotareas. LAA offers an alternative for operators to make use of unlicensedspectrum while managing one radio network, thus offering newpossibilities for optimizing the network's efficiency.

In an example embodiment, Listen-before-talk (clear channel assessment)may be implemented for transmission in an LAA cell. In alisten-before-talk (LBT) procedure, equipment may apply a clear channelassessment (CCA) check before using the channel. For example, the CCAmay utilize at least energy detection to determine the presence orabsence of other signals on a channel in order to determine if a channelis occupied or clear, respectively. For example, European and Japaneseregulations mandate the usage of LBT in the unlicensed bands. Apart fromregulatory requirements, carrier sensing via LBT may be one way for fairsharing of the unlicensed spectrum.

In an example embodiment, discontinuous transmission on an unlicensedcarrier with limited maximum transmission duration may be enabled. Someof these functions may be supported by one or more signals to betransmitted from the beginning of a discontinuous LAA downlinktransmission. Channel reservation may be enabled by the transmission ofsignals, by an LAA node, after gaining channel access via a successfulLBT operation, so that other nodes that receive the transmitted signalwith energy above a certain threshold sense the channel to be occupied.Functions that may need to be supported by one or more signals for LAAoperation with discontinuous downlink transmission may include one ormore of the following: detection of the LAA downlink transmission(including cell identification) by UEs; time & frequency synchronizationof UEs.

In an example embodiment, DL LAA design may employ subframe boundaryalignment according to LTE-A carrier aggregation timing relationshipsacross serving cells aggregated by CA. This may not imply that the eNBtransmissions can start only at the subframe boundary. LAA may supporttransmitting PDSCH when not all OFDM symbols are available fortransmission in a subframe according to LBT. Delivery of necessarycontrol information for the PDSCH may also be supported.

A LBT procedure may be employed for fair and friendly coexistence of LAAwith other operators and technologies operating in unlicensed spectrum.LBT procedures on a node attempting to transmit on a carrier inunlicensed spectrum require the node to perform a clear channelassessment to determine if the channel is free for use. An LBT proceduremay involve at least energy detection to determine if the channel isbeing used. For example, regulatory requirements in some regions, e.g.,in Europe, specify an energy detection threshold such that if a nodereceives energy greater than this threshold, the node assumes that thechannel is not free. While nodes may follow such regulatoryrequirements, a node may optionally use a lower threshold for energydetection than that specified by regulatory requirements. In an example,LAA may employ a mechanism to adaptively change the energy detectionthreshold, e.g., LAA may employ a mechanism to adaptively lower theenergy detection threshold from an upper bound. Adaptation mechanism maynot preclude static or semi-static setting of the threshold. In anexample Category 4 LBT mechanism or other type of LBT mechanisms may beimplemented.

Various example LBT mechanisms may be implemented. In an example, forsome signals, in some implementation scenarios, in some situations,and/or in some frequencies no LBT procedure may performed by thetransmitting entity. In an example, Category 2 (e.g. LBT without randomback-off) may be implemented. The duration of time that the channel issensed to be idle before the transmitting entity transmits may bedeterministic. In an example, Category 3 (e.g. LBT with random back-offwith a contention window of fixed size) may be implemented. The LBTprocedure may have the following procedure as one of its components. Thetransmitting entity may draw a random number N within a contentionwindow. The size of the contention window may be specified by theminimum and maximum value of N. The size of the contention window may befixed. The random number N may be employed in the LBT procedure todetermine the duration of time that the channel is sensed to be idlebefore the transmitting entity transmits on the channel. In an example,Category 4 (e.g. LBT with random back-off with a contention window ofvariable size) may be implemented. The transmitting entity may draw arandom number N within a contention window. The size of contentionwindow may be specified by the minimum and maximum value of N. Thetransmitting entity may vary the size of the contention window whendrawing the random number N. The random number N is used in the LBTprocedure to determine the duration of time that the channel is sensedto be idle before the transmitting entity transmits on the channel.

LAA may employ uplink LBT at the UE. The UL LBT scheme may be differentfrom the DL LBT scheme (e.g. by using different LBT mechanisms orparameters) for example, since the LAA UL is based on scheduled accesswhich affects a UE's channel contention opportunities. Otherconsiderations motivating a different UL LBT scheme include, but are notlimited to, multiplexing of multiple UEs in a single subframe.

In an example, a DL transmission burst may be a continuous transmissionfrom a DL transmitting node with no transmission immediately before orafter from the same node on the same CC. An UL transmission burst from aUE perspective may be a continuous transmission from a UE with notransmission immediately before or after from the same UE on the sameCC. In an example, UL transmission burst is defined from a UEperspective. In an example, an UL transmission burst may be defined froman eNB perspective. In an example, in case of an eNB operating DL+UL LAAover the same unlicensed carrier, DL transmission burst(s) and ULtransmission burst(s) on LAA may be scheduled in a TDM manner over thesame unlicensed carrier. For example, an instant in time may be part ofa DL transmission burst or an UL transmission burst.

The following signals or combination of the following signals mayprovide functionality for the UE's time/frequency synchronization forthe reception of a DL transmission burst in LAA SCell(s): a) servingcell's DRS for RRM measurement (DRS for RRM measurement may be used atleast for coarse time/frequency synchronization), b) reference signalsembedded within DL transmission bursts (e.g. CRS and/or DMRS), and/or c)primary/secondary synchronization signals. If there is an additionalreference signal, this signal may be used. Reference signals may be usedat least for fine time/frequency synchronization. Other candidates(e.g., initial signal, DRS) may be employed for synchronization.

DRS for RRM may also support functionality for demodulation of potentialbroadcast data multiplexed with DRS transmission. Other mechanism orsignals (e.g., initial signal, DRS) for time/frequency synchronizationmay be needed to support reception of DL transmission burst.

In an example embodiment, DRS may be used at least for coarsetime/frequency synchronization. Reference signals (e.g., CRS and/orDMRS) within DL transmission bursts may be used at least for finetime/frequency synchronization. Once the UE detects DRS and achievescoarse time/frequency synchronization based on that, the UE may keeptracking on the synchronization using reference signals embedded inother DL TX bursts and may also use DRS. In an example, a UE may utilizeDRS and/or reference signals embedded within a DL transmission bursttargeting the UE. In another example, a UE may utilize DRS and/orreference signals embedded within many available DL transmission burstsfrom the serving cell (to the UE and other UEs).

The discovery signal used for cell discovery/RRM measurement (e.g.opportunistic transmission within configured DMTC) may be used formaintaining at least coarse synchronization with the LAA cell (e.g. <±3μs timing synchronization error and <±0.1 ppm frequency synchronizationerror). DRS may be subject to LBT. Inter-DRS latency generally getsworse as Wi-Fi traffic load increases. It is noted that the inter-DRSlatency can be rather significant. In example scenario, there may be aprobability of approximately 55% that the inter-DRS latency is 40 ms andthere may be a probability of approximately 5% that inter-DRS latency is≥440 ms. The inter-DRS latency as seen by the UE may be worseconsidering the possibility of misdetection by the UE. Discovery signalmisdetection may be due to actual misdetection or due to UE unavailablefor detection because of DRX inter-frequency measurement during DMTCoccasion.

Depending on LAA DRS design, OFDM symbol boundary may be obtained byDRS. PCell and SCell timing difference may be kept on the order of ±30usec. The aggregated cells may be synchronized to some extent, e.g.aligned frame timing and SFN. Thus, similar requirement may be appliedto the PCell and LAA cells on the unlicensed band. In an example, a UEmay not utilize timing and frequency of the PCell for coarsesynchronization of LAA cells since the timing offset may be up to ˜30 us(e.g. non-located) and a frequency reference may not be reliable due tothe band distance between PCell and LAA cell (2 GHz Pcell and 5 GHz LAAcell). PCell timing information also may be used for timesynchronization at subframe or frame level. SCell(s) may employ the sameframe number and subframe number as the PCell.

PCell timing information may provide some information for symbolsynchronization. By synchronizing PCell, frequency difference observedby UE between PCell and LAA Scell may be up to 0.6 ppm. For example,after 300 ms, the amount of the time drift may be 0.18 usec at most. ForLAA, path delay may be relatively small as the target coverage is small.With timing drift, the multi-path delay may be within cyclic prefixlength.

According to some of the various aspects of embodiments, a UE mayutilize a licensed band carrier as a reference for time/frequencysynchronization for CA of licensed carrier and unlicensed carrier, forexample when they are in the same group (e.g. co-located). Whennon-collocated eNBs support licensed band PCell and unlicensed bandSCell separately in a CA scenario, there may exist maximum ˜30 us timingdifference between PCell and unlicensed band SCell. In an exampleembodiment, the frequency difference between the UE synchronized withPCell and unlicensed band SCell may observe at most 0.6 ppm. An LAA mayprovide functionality for time/frequency synchronization on unlicensedband at least for non-collocated CA scenario.

Example reasons for a frequency difference may be: 1) oscillatordifference among PCell, SCell and UE, 2) Doppler shift and 3) fastfading aspect. The oscillator difference of 0.6 ppm offset in 5 GHzcorresponds to 3 kHz offset. Subcarrier spacing of LTE numerology may be15 kHz. This offset may need to be taken into account before FFToperation. One of the reasons of oscillator frequency variation istemperature. If the frequency difference is not obtained at the point ofDRS reception, a UE may need to buffer subsequent data transmissionuntil the UE obtains this frequency difference before FFT. The frequencyoffset caused by this may be obtained at the reception of DRS. Dopplershift may be small value for a low mobility UE. Fast fading and residualmismatch caused by 1) and 2) may be compensated during a demodulationprocess similar to a licensed band. This may not require introducingadditional reference signals for unlicensed band.

According to some of the various aspects of embodiments, a UE may beconfigured to perform inter-frequency measurements on the carrierfrequency layer using measurement gaps for SCells that are notconfigured yet. An SCell receiver may not be turned on and measurementsmay be performed using the Pcell receiver. When a cell is added as anScell but not activated (“deactivated state”), the UE may receiverelevant system information for the SCell from the Pcell. UE may beconfigured to perform measurements on the Scell without measurementgaps. An SCell receiver may need to be occasionally turned on (e.g. for5 ms every 160 ms) for RRM measurements using either CRS or Discoverysignals. Cells may be added as an Scell and activated (“activatedstate”), then the UE may be ready to receive PDSCH on the Scell in allsubframes. The SCell receiver may perform (E)PDCCH monitoring in everysubframe (for a self-scheduling case). An SCell receiver may bufferevery subframe for potential PDSCH processing (for both self andcross-carrier scheduling cases).

The eNodeB may configure the UE to measure and report RRM measurements(e.g. including RSSI) on a set of carrier frequencies. Once a suitablecarrier or a set of suitable carriers is determined, carrier selectedmay be added as an SCell by RRC (e.g. with ˜15 ms configuration delay),followed by SCell activation (with ˜24 ms delay). If an SCell isdeactivated, the UE may assume that no signal is transmitted by the LAAcell, except a discovery signal may be transmitted when configured. Ifan SCell is activated, the UE may be required to monitor PDCCH/EPDCCHand perform CSI measurement/reporting for the activated SCell. In aU-cell, a UE may not assume that every subframe of activated LAA SCellcontains transmission. For LAA carriers, channel access may depend onthe LBT procedure outcome. The network may configure and activate manycarriers for the UE. The scheduler may then dynamically selectcarrier(s) for DL assignment or UL grant transmission.

According to some of the various aspects of embodiments, the first stageof cell level carrier selection may be during an initial set up of acell by an eNB. The eNB may scan and sense channels for interference orradar detection. The eNB may configure the SCells accordingly based onthe outcome of its carrier selection algorithm for efficient loadbalancing and interference management. The carrier selection process maybe on a different time scale from the LBT/CCA procedure prior totransmissions on the carriers in unlicensed spectrum. The RSSImeasurement report from the UE may be used to assist the selection ateNB.

According to some of the various aspects of embodiments, the secondstage of cell level carrier selection is after initial set up. Themotivation is that an eNB may need to do carrier (re)selection due tostatic load and interference change on some carriers, e.g., a new Wi-FiAP is set up and continuously accesses the carrier causing relativelystatic interference. Therefore, semi-static carrier selection may bebased on the eNB sensing of the averaged interference level, potentialpresence of radar signals if required, and traffic load on the carriersover a relatively longer time scale, as well as RRM measurement from UEsin the cell. Due to the characteristics in unlicensed spectrum, RRMmeasurements on LAA SCells may be enhanced to support better carrierselection. For example, the RSSI measurement may be enhanced usingoccupancy metric indicating the percentage of the time when RSSI isabove a certain threshold. It may be noted that cell level carrierselection may be a long-term (re)selection since the process may berather costly due to the signalling overhead and communicationinterruptions for UEs in a cell and it may also affect the neighboringcells. Once a suitable set of carriers is identified, they may beconfigured and activated as SCells for UEs. This process may becontinuous in order to keep reassessing the interference environment.Cell-level carrier selection in unlicensed spectrum may be a relativelylong-term (re)selection based on eNB sensing and RRM measurement reportfrom UE. RRM measurement on LAA SCells may be enhanced to support bettercarrier selection.

Carrier selection from a UE perspective may be to support carrierselection for a UE among the set of carriers that the eNB has selectedat the cell level. Carrier selection for the UE in unlicensed spectrummay be achieved by configuring a set of the carriers on which the UEsupports simultaneous reception and transmission. The UE may perform RRMmeasurements on the configured carriers and report them to the eNB. TheeNB may then choose which of the carriers to activate and use fortransmission when it has pending data for the UE. The number of carriersto activate may then also be chosen based on the data rate needed andthe RRM measurements for the different carriers. The activation delayfor a carrier before scheduling data on it may be up to ˜24 ms, assumingthat the UE has performed RRM measurement on this carrier prior toreceiving the activation command within DRX cycle. By operating thecarrier selection based on activation and deactivation, the selectionmay also be done in the order of tens of msec.

According to some of the various aspects of embodiments, CRS may not betransmitted in an activated subframe when a burst is not scheduled inthat subframe. If there are no transmissions from the eNB for anextended duration (Toff), UE demodulation performance may be impacteddue to lack of reference symbols for fine time/frequency tracking. Theextent of performance impact may depend on the amount of time for whichthere are no eNB transmissions. The impact may be mitigated by morefrequent transmission of discovery signals.

Discovery signals may be transmitted by the eNB even when UEs are notbeing scheduled. Setting discovery signal periodicity based on UE RRMmeasurement requirements (e.g. 160 ms) may be more efficient thansetting the periodicity based on UE fine time/frequency trackingrequirement.

In an example embodiment, Scell deactivation timer for the unlicensedScell may be set to a value closer to (Toff) based on UE finetime/frequency tracking requirements. This may result in more frequenttransmission of activation commands. Activation commands may be neededwhen the eNB has data to schedule to a UE. From the UE perspective,after receiving an activation command in a particular subframe, the UEmay receive CRS in a number (e.g. one or two) of the followingsubframes. The UEs may receive CRS transmissions for a few symbols orsubframes, which they may use for settling AGC loop and time-frequencytracking filters before PDSCH reception on the SCell. UEs may receiveCRS transmission (e.g. in a few OFDM symbols) between reception ofactivation command and reception PDSCH on the Scell.

Activating a large number of carriers on dynamic bases may increase theUE power consumption, false alarm probability, and processing powerrequirements. Improved mechanisms are needed to improve efficiency inthe UE and enable fast and dynamic carrier selection/activation in a UE.Novel mechanisms may reduce UE power consumption, reduce false alarmprobability and reduce processing power requirements. Carrier selectionand activation may be enhanced to achieve fast dynamic carrier selection(or switching). A fast activation procedure for the carrier (e.g.shorter than the currently defined 24 ms) may be defined to improveefficiency.

Current SCell activation latency may include the MAC CE decoding latency(˜3-6 ms) and SCell activation preparation time (RF preparation, up to˜18 ms). Implementation of faster processes and hardware may reducethese delays. SCell MAC activation/deactivation signalling may beUE-specific. Signalling overhead may be a concern especially if the cellused for transmitting the signal is a macro cell. In an exampleembodiment, a L1 procedure/indicator may be introduced and/or SCellactivation signalling may be enhanced.

Layer one signalling (e.g. PDCCH/EPDCCH from the PCell or anotherserving cell) may be implemented to signal the set of carriers that theUE may monitor for PDCCH/EPDCCH and/or measuring/reporting CSI. Controlsignalling latency may be ˜2 ms (e.g. one 1 ms EPDCCH transmission plus0.5 ms decoding). The DCI format may be of small size for transmissionreliability and overhead reduction. To reduce control signallingoverhead, the signalling may be a UE-common signalling. The indicationmay be sent on a carrier that the UE is currently monitoring.

In an example embodiment, a mechanism based on a L1 indication forstarting/stopping monitoring of up to k activated carriers may beprovided. The UE may be configured with n>=k CCs. k CCs may be activatedvia MAC signalling of SCell activation/deactivation. Based on LBTprogress over the CCs, a L1 indication may be sent to inform which ofthe k CCs may be monitored by the UE and which may not. The UE may thenreceive data burst(s) on the monitored CCs. Another L1 indication may besent after the bursts to alter which CCs may be monitored since then,and so on. The L1 indication may be explicit (e.g., based on asignalling) or implicit (e.g., based on self-scheduling and UE detectionof scheduling information on the SCell). For this example, fast carrierswitching is done among at most k CCs.

In an example embodiment, a mechanism based on a L1 signalling forstarting/stopping monitoring of up to m activated carriers (the numberof p configured carriers may be m or higher). The activated carriers maybe more than n (e.g., there may be more CCs activated for the UE thanits PDSCH aggregation capability-n). The UE is configured with p CCs,and there may be up to m CCs that are activated via MAC signalling ofSCell activation/deactivation. The UE may not monitor all the activatedCCs. The UE may monitor at most n CCs according a L1 indication. The L1indication needs to be explicit rather than implicit, since an implicitindication may require a UE to monitor all the up to m activatedcarriers at the same time, exceeding the UE's capability. For thisexample, fast carrier switching is done among possibly more than n CCs.

According to some of the various aspects of embodiments, SCellactivation/deactivation enhancements may be considered for fast carrierswitching. SCell activation/deactivation signalling is a MAC signalling.MAC signalling decoding/detection (with or without enhancements) may beslower than L1 signalling decoding/detection. It may involvedecoding/detection of a L1 signalling and furthermore, a PDSCH. If SCellactivation/deactivation is carried by a L1 signalling, it may still beconsidered for fast carrier switching. In an example embodiment, amechanism based on a L1 signalling for activation/deactivation of the pconfigured carriers. The UE is configured with p CCs, but each timethere are at most n CCs are activated via a L1 signalling of SCellactivation/deactivation. For instance, based on LBT progress over theCCs, a L1 signalling may be sent to inform which of the p CCs areactivated. The UE may receive data burst(s) on the activated CCs.Another L1 signalling may be sent after the bursts to alter theactivated CCs. For this example, fast carrier switching may be doneamong possibly more than n CCs.

The control signalling may be transmitted before the eNB has gainedaccess to the carrier via LBT process. An eNB may inform the UE to start(or stop) monitoring a carrier (whether the UE would receive a burst ornot depends on the presence of PDCCH scheduling information for thecarrier). An indication for starting monitoring may be used for morethan one burst, until an indication for stopping monitoring is sent. Theindication may be sent when the eNB expects the (E) CCA is to completesoon. A purpose of the indication may be to inform a UE to start or stopmonitoring a carrier.

Transmitting the control signalling after the eNB has gained access tothe carrier may incur overhead of the reservation signal (proportionalto the control signalling latency). In an example, the maximumtransmission burst may be 4 ms. An eNB may inform the UE to receive aburst on a carrier. The eNB may send one indication for a burst. Theremay be many short bursts (e.g., one burst may last up to 4 millisecondsin certain regions). The indication may be sent after (E)CCA iscompleted, consuming some portion of the maximum allowed transmissionduration for a burst.

It may still be up to the network to transmit the control signallingbefore or after the channel is occupied. A UE may detect that the burstis from the serving cell (e.g. by confirming PCID). A function of thecontrol signalling may be to indicate that the UE may perform DLtransmission burst detection of the serving cell. If a DL burst of theserving cell is detected, the UE may monitor for possible PDCCH/EPDCCHand/or measuring the CSI on the indicated SCell.

In an example embodiment, a UE may be configured with a number ofcarriers potentially exceeding the maximum number of carriers over whichthe UE may aggregate PDSCH. RRM measurements over the configuredcarriers may be supported, e.g. RSSI-like measurement, extension ofquasi co-location concept to across collocated intra-band carriers,and/or carrier grouping. L1 indication to the UE to start monitoring acarrier, which is selected from the configured carriers by the eNB maybe supported.

According to some of the various aspects of embodiments, an eNB mayconfigure a UE with more component carriers which may potentially exceedthe maximum number of carriers over which the UE may aggregate PDSCH.eNB may activate one or more carriers among the configured carriers tothe UE by the existing signalling, e.g. MAC signalling. The UE may bescheduled on the one or more activated carriers dynamically based on theLBT mechanism.

A UE may switch to receive on any carrier within a set of carriersselected by the serving eNB as fast as subframe/symbol-level, while thenumber of carriers within the set may potentially exceed the maximumnumber of carriers over which the UE may aggregate PDSCH. Whichcarrier(s) the UE may switch to is per eNB indication. When the UE isindicated with the carrier(s) it may switch to, the UE may start tomonitor the indicated carrier(s), e.g. within a few subframes, and maystop monitoring other carriers. By monitoring a carrier, it meant tobuffer and attempt to detect the control channels and other associatedchannels. The eNB indication may instruct the UE to switch to theindicated carrier(s) and monitor the carrier(s). The eNB may notinstruct the UE to switch to monitor on more carriers than its PDSCHaggregation capability in a given subframe. The eNB may not schedule theUE on more carriers than its PDSCH aggregation capability. SCellconfiguration enhancements may allow both semi-static and fast carrierswitching with reduced transition time. The delay associated with theSCell configuration signalling as well as the delay associated with themeasurement process may be decreased.

In an example embodiment, fast carrier switching may support a UE toswitch to any carrier within a set of carriers selected by the servingeNB as fast as a few subframes/symbols. The eNB may send an indicationinstructing the UE to switch to the indicated carriers and monitor thecarriers. Then the UE may perform the switching and start monitoring theindicated carriers. The UE stops monitoring other carriers. The eNBindication may be done in L1. A L1 procedure/indicator, or anenhancement of the SCell activation signalling may be introduced.

According to some of the various aspects of embodiments, DRS design mayallow DRS transmission on an LAA SCell to be subject to LBT. Thetransmission of DRS within a DMTC window if LBT is applied to DRS mayconsider many factors. Subjected to LBT, DRS may transmitted in fixedtime position within the configured DMTC. Subject to LBT, DRS may betransmitted in at least one of different time positions within theconfigured DMTC. The number of different time positions may berestricted. One possibility is one-time position in the subframe. DRStransmissions outside of the configured DMTC may be supported.

According to some of the various aspects of embodiments, a sensinginterval may allow the start of a DL transmission burst (which may notstart with the DRS) containing DRS without PDSCH within the DMTC. Totalsensing period may be greater than one sensing interval. Whether theabove may be used for the case where transmission burst may not containPDSCH but contains DRS, and any other reference signals or channels. TheECCA counter used for LBT category 4 for the PDSCH may be frozen duringDL transmission burst containing DRS without PDSCH

The RS bandwidth and density/pattern of the DRS design for LAA maysupport for RRM measurement based on a single DRS occasion.

According to some of the various aspects of embodiments, Discoverysignal may be transmitted via a successful LBT operation. When the eNBdoes not have access to the channel, the discovery signal burst may notbe transmitted. In an example, the discovery signal periodicity isconfigured to be 40 ms, and it may be possible to receive the discoverysignal at least once in every 160 to 200 ms with a high probability. Forexample, the probability of receiving a discovery signal burst at leastonce in every 160 ms may greater than 97%. The UE may adjust itsreceiver processing to account for the potential absence of discoverysignals due to lack of access to the channel. For instance, the UE maydetect the presence or absence of a particular discovery signal burstusing the PSS, SSS and CRS signals.

According to some of the various aspects of embodiments, the use ofdiscovery signals that may be subject to LBT. A discovery signal burstmay not be transmitted when LBT fails. Data may be transmitted in theintervening subframes. The reference signals along with controlinformation may be used to reserve the channel prior to a discoverysignal or data transmission.

For reception of data on the serving cell, AGC and fine time andfrequency estimation may employ the discovery signals from the servingcell. In an example, time and frequency estimation may be performedusing the PSS, SSS and/or CRS inside the discovery signal subframes. Theuse of two or more CRS ports may enhance synchronization performance.These signals may provide synchronization estimates that are adequatefor the purpose of RRM measurements on the serving and neighboringcells. When data is to be received by the UE in a subframe that occurs asignificant number of subframes after the last reception of a discoverysignal on the serving cell. Fine tuning of the time and frequencyestimates may be performed using the DM-RS and, if present, the CRSwithin the subframe in which data is received, and/or the initialsignal. The signal used to reserve the channel before the actual startof data transmissions (e.g. reservation signal, initial signal, and/orburst indicator) may be used to fine tune time and frequency estimatesbefore the reception of data. When transmitting data after a longabsence of any discovery signal or other transmissions, the eNB maytransmit a signal of longer duration to reserve the channel in order tofacilitate the use of such a signal for timing and frequencyadjustments.

According to the latest release of 3GPP standards (e.g. 3GPP TS 36.300,3GPP TS 36.331, 3GPP TS 36.321) each TAG must contain at least oneserving cell with a configured uplink. Each configured cell must beincluded in the primary TAG or a secondary TAG. The parameter sTAG-Id inMAC-MainConfigSCell configured for an SCell indicates the TAG of anSCell. The parameter sTAG-Id uniquely identifies the TAG within thescope of a Cell Group (e.g. MCG or SCG). If the field is not configuredfor an SCell (e.g. absent in MAC-MainConfigSCell), the SCell is part ofthe pTAG.

According to the latest release of 3GPP TS 36.300, in RRC_CONNECTED, theeNB is responsible for maintaining the timing advance. Serving cellshaving UL to which the same timing advance applies (typicallycorresponding to the serving cells hosted by the same receiver) andusing the same timing reference cell are grouped in a timing advancegroup (TAG). Each TAG contains at least one serving cell with configureduplink, and the mapping of each serving cell to a TAG is configured byRRC. In case of DC, a TAG only includes cells that are associated to thesame eNB and the maximum number of TAG is 8. In some cases (e.g. duringDRX), the timing advance is not necessarily always maintained and theMAC sublayer knows if the L1 is synchronized and which procedure to useto start transmitting in the uplink: as long as the L1 isnon-synchronized, uplink transmission may only take place on PRACH.

For a TAG, cases where the UL synchronization status moves from“synchronized” to “non-synchronized” include: Expiration of a timerspecific to the TAG; Non-synchronized handover.

The synchronization status of the UE follows the synchronization statusof the pTAG of MCG. The synchronization status of the UE w.r.t. SCGfollows the synchronization status of the pTAG of SCG. When the timerassociated with pTAG is not running, the timer associated with a sTAG inthat CG may not be running. Expiry of the timers associated with one CGdoes not affect the operation of the other CG.

The value of the timer associated to the pTAG of MCG is either UEspecific and managed through dedicated signalling between the UE and theeNB, or cell specific and indicated via broadcast information. In bothcases, the timer is normally restarted whenever a new timing advance isgiven by the eNB for the pTAG: restarted to a UE specific value if any;or restarted to a cell specific value otherwise.

The value of the timer associated to a pTAG of SCG and the value of atimer associated to a sTAG of a MCG or a sTAG of SCG are managed throughdedicated signalling between the UE and the eNB, and the timersassociated to these TAGs may be configured with different values. Thetimers of these TAGs may be restarted whenever a new timing advance isgiven by the eNB for the corresponding TAG.

Upon DL data arrival or for positioning purpose, a dedicated signatureon PRACH may be allocated by the eNB to the UE. When a dedicatedsignature on PRACH is allocated, the UE may perform the correspondingrandom access procedure regardless of its L1 synchronization status.

Timing advance updates are signalled by the eNB to the UE in MAC PDUs.

The UE may have capability to follow the frame timing change of theconnected eNode B. The uplink frame transmission takes place(N_(TA)+N_(TAoffset))×T_(s) before the reception of the first detectedpath (in time) of the corresponding downlink frame from the referencecell. The UE may be configured with a pTAG containing the PCell. ThepTAG may also contain one or two SCells, if configured. The UE capableof supporting multiple timing advance may also be configured with onesTAG, in which case the pTAG may contain the PCell and the sTAG maycontain one or more SCells. The UE capable of supporting dualconnectivity may be configured with one pTAG and may also be configuredwith one psTAG. The pTAG may contain the PCell and the psTAG may containthe PSCell.

3GPP TR 36.889 V13.0 (2015 June) is a Technical Report published by 3rdGeneration Partnership Project, in Technical Specification Group RadioAccess Network. 3GPP TR 36.889 is entitled “Study on Licensed-AssistedAccess to Unlicensed Spectrum” and is a technical report for Release 13of LTE-Advanced technology. The purpose of the TR is to document theidentified LTE enhancements and corresponding evaluations for a singleglobal solution framework for licensed-assisted access to unlicensedspectrum.

The Rel-13 Work Item on Licensed-Assisted Access to Unlicensed Spectrum(LAA) has been approved in RAN#68, 3GPP document RP-151045 in June 2015,to “only specify support for LAA SCells operating with only DLtransmissions.” Uplink transmission capabilities may be added to laterreleases, e.g., Rel-14.

In some example embodiments, TAG mechanisms are described when LAA(unlicensed) SCells with DL only transmission are configured. In someexample embodiments, TAG mechanisms are described when LAA-SCells withboth DL and UL transmission are configured. The synchronization issuesfor LAA cells are addressed and example mechanisms for enhancingsynchronization in a multi carrier configuration are presented.

According to the latest LTE-Advanced standard specification, each TAGcontains at least one serving cell with configured uplink, and themapping of each serving cell to a TAG is configured by RRC. Eachconfigured cell must be included in the primary TAG or a secondary TAG.The parameter sTAG-Id in MAC-MainConfigSCell configured for an SCellindicates the TAG of an SCell. If the field is not configured for anSCell (e.g. absent in MAC-MainConfigSCell), the SCell is part of thepTAG.

LTE-A Rel-13 may specify support for LAA SCells operating with only DLtransmissions. The cells with no configured uplink may not have a timingadvance. There is no uplink transmission for SCell(s) with no configureduplink. According to the current principles, LAA cells with noconfigured uplink may be assigned to a TAG that includes at least oneother cell with a configured uplink. In an example embodiment, LAA cellsmay not be configured with mac-MainConfigSCell, and as a result may beconsidered belonging to a pTAG. Since pCell is always configured with anuplink, pTAG containing LAA cells (without uplink) contain a cell(pCell) with configured uplink. Some example embodiments provide methodsand systems for TAG configuration of DL only LAA cells. Some exampleembodiments provide methods and systems to enhance synchronization forDL only LAA cells. Some example embodiments provide methods and systemsto enhance uplink transmission timing of unlicensed (e.g. LAA) cells.Example embodiments of the invention enhances synchronization ofdownlink and/or uplink signals when LAA cells are configured as a partof pTAG and/or sTAG.

In an example embodiment, LAA cell(s) may transmit signals from atransmission point located at a different location compared with theprimary cell. The subframe reception timing of LAA cell and pCell may bedifferent, e.g. due to propagation delay, and/or synchronization errorsbetween two different transmission points. If mac-MainConfigSCell is notconfigured for a LAA cell, the cell may be configured as a part of thepTAG, even though downlink reception timing of pCell may not besynchronized with downlink reception timing of the LAA cell in a UEreceiving signals from both cells. That may not be an issue whensynchronization (e.g. fine synchronization) of received signals fromSCell and pCell are done separately in a UE receiver.

In a scenario, wherein multiple LAA cells are configured on atransmission point different from the pCell, configuration of those LAAcells as a part of the pCell may result in non-optimal configurations.For example, multiple DL-only LAA cells may be transmitted from a giventransmission point and have the same downlink timing difference. Thedownlink timing of these DL-only cells may be different from the timingof a pCell transmitted from a different transmission point. In such ascenario, synchronization at symbol level (e.g. fine synchronization)for LAA cells may not be based on the signals received from the pCell.

Synchronization of signals received from an LAA cell may be moredifficult compared with synchronization of signals received on alicensed cell. For example, synchronization and reference signaltransmission by an eNB on an LAA cell is subject to LBT. For example, aneNB may not be able to transmit synchronization signals in manyinstances on a congested and/or interfered cell.

In an example embodiment, LAA cells transmitted from the sametransmission point may be synchronized. A UE may receive signals ofthese LAA cells with the same timing. For example, one or more instanceof synchronization signals and/or reference signals received on one ofthe LAA cells may be used for synchronizing one or more LAA cellstransmitted from the same transmission point. This mechanism in a UE mayprovide many advantages in synchronizing to an LAA cell when multipleLAA cells are configured on the same transmission point. The cells fromthe same transmission point may be in the same band. Signals of cells inthe same band and the same transmission point may be synchronized toeach other and received via the same transceiver.

In an example embodiment, DL only LAA cells may be configured as a partof the pTAG or sTAG. The parameter sTAG-Id in MAC-MainConfigSCell may beconfigured for a DL-only SCell and indicate the TAG of the DL-only LAASCell. DL only LAA cells do not transmit uplink signals. In an example,TAG configuration may be employed for enhancing downlink synchronizationfor LAA cell(s). In an example, a TAG may not necessarily include a cellwith a configured uplink. The latest release of LTE-Advancedspecification teaches away from such a configuration. In an examplescenario, such a configuration may enhance downlink synchronization inLAA cells.

A wireless device may receive at least one (RRC) message comprisingconfiguration parameters of a plurality of cells grouped into aplurality of cell groups comprising a first cell group and a second cellgroup. The plurality of cells consisting of: a plurality ofdownlink-uplink cells, each of the plurality of downlink-uplink cellshaving a configured uplink and a configured downlink; and at least onedownlink-only cell, each of the at least one downlink-only cell having aconfigured downlink with no configured uplink. The wireless device mayreceive at least one timing advance command comprising: a timeadjustment value and an index of the first cell group. The wirelessdevice may apply the timing advance command to uplink transmissiontiming of at least one downlink-uplink cell in the first cell group.

In an example, the second cell group may be configurable to consist ofone or more downlink-only cells only if the one or more downlink-onlycells are unlicensed cells. In an example, the second cell group may beconfigurable to consist of one or more downlink-only cells only if thewireless device has a first capability, for example support LAA cells,supports LAA cells with certain configuration, is compatible with acertain LTE release, and/or support enhanced configuration, and/or thelike.

If the one or more downlink-only cells are licensed cells, the secondcell group may comprise one or more downlink-uplink cells in theplurality of downlink-uplink cells. The first cell group may comprise afirst subset of the plurality of cells. Uplink transmission timing inthe first cell group being derived employing a first cell in the firstcell group. In an example, time alignment timer of the second cell groupmay be disabled/released or set to infinity when the second cell groupconsists of the one or more downlink-only cells. In an example, timealignment timer may not be configured for the second cell group when thesecond cell group consists of the one or more downlink-only cells.

In an example embodiment, the second cell group may be configurable toconsist of one or more downlink-only cells only if the wireless devicehas a first capability. For example, if the wireless device supportsunlicensed cells, or certain configuration of unlicensed cells. In anexample, the wireless device includes a certain IE in the capabilitymessage transmitted to the base station indicating support for suchfeature, for example, when the wireless device supports a new carriertype or an enhanced carrier configuration. For example, if the wirelessdevice is a release 13/14/15, and/or beyond wireless device. If thewireless device does not have a first capability, the second cell groupmay comprise one or more downlink-uplink cells in the plurality ofdownlink-uplink cells. If the wireless device does not have a firstcapability, the legacy TAG rules on cell configurations in a group mayapply. When a cell is de-activated, synchronization is needed to decodeDRS signal, when DRS is configured. When a cell is de-activated,synchronization is needed to decode synchronization, CRS, and/or CSI-RSsignals (e.g. for RRM measurement), if DRS is not configured. Ifbroadcast data is received along with DRS, DRS signal may be used tofine synchronize the receiver to decode the downlink broadcast data.Fine synchronization is needed to decode downlink bursts (when a cell isactivated). Example embodiments may be implemented when a cell isdeactivated, to enhance synchronization to decode received signals,e.g., DRS signals. Example embodiments may be implemented when a cell isactivated, to enhance synchronization to decode DRS signals, CSI-RSand/or downlink bursts.

In an example embodiment, a type of grouping may be introduced tosupport downlink synchronization for unlicensed cells. For example,unlicensed cells transmitted from the same transmission point and/orfrom the transmitted in the same band may be grouped in a group. An RRCmessage may comprise one or more parameters indicating the downlinkgrouping of unlicensed cells. For example, an identifier such as a groupindex, a reference cell index, a band index, or a transmission pointindex may be introduced to identify the group. Cells in the group mayperform downlink synchronization jointly to enhance downlinksynchronization. In an example, embodiment the TAG grouping may beemployed for downlink synchronization in a group.

The wireless device may receive at least one control message comprisingconfiguration parameters of a plurality of cells comprising two or moreunlicensed cells comprising a first unlicensed cell and a secondunlicensed cell. The wireless device may synchronize a reception timingof the first unlicensed cell employing at least a second received signalof the second unlicensed cell. The wireless device may synchronize areception timing of the second unlicensed cell employing at least afirst received signal of the first unlicensed licensed cell. A pluralityof cells may be grouped. Downlink synchronization of the cells in thegroup may be performed employing signals of more than one of cells inthe group. An example process is illustrated in FIG. 13. Synchronizationsignal, discovery signal and/or reference signal of more one cell may beemployed for synchronization of downlink signals of a cell. Thesynchronization may be at the symbol level (e.g. fine downlinksynchronization and/or coarse synchronization level).

In an example embodiment, downlink synchronization of an LAA cell mayemploy downlink signals of a licensed cell transmitted from the sametransmission point and configured in the same TAG (or another type ofgroup). In an example embodiment, downlink synchronization of an LAAcell may employ downlink signals of another LAA cell transmitted fromthe same transmission point configured in the same group.

In an example embodiment, a TAG may or may not include a cell with aconfigured uplink. For example, DL only LAA cells transmitted from thesame transmission point may be configured in a TAG without a cell with aconfigured uplink. In an example embodiment, a DL only cell and a DLonly LAA cell transmitted from the same transmission point may beconfigured in a TAG without a cell with a configured uplink. Suchmechanisms may enhance downlink synchronization in a multi carrierconfiguration, e.g. when LAA cell(s) are configured. For example, theLAA cell may employ the signals received on the licensed cell (e.g. inaddition to received signals on the LAA cell) to enhance downlinksynchronization.

Enhancing TAG configuration to support/enhance downlink synchronizationand improve uplink synchronization may improve synchronizationmechanisms in a multi-carrier technology. Some example embodimentsenhance the TAG configuration and processes/mechanisms.

In some example embodiments, a different type of grouping may beintroduced for improving downlink synchronization. The processesintroduced for enhancing TAG configuration may be implemented in adifferent type of grouping. In some example implementations, a cellgroup is called a TAG. Other naming conventions may be used instead of aTAG, such as a synchronization group, a downlink synchronization group,a cell group, a timing group, and/or the like.

FIG. 10 is a diagram depicting downlink reception timing of one or morecells in a first timing advance group (TAG1) and a second TAG (TAG2) asper an aspect of an embodiment of the present invention. TAG1 mayinclude one or more cells, TAG2 may also include one or more cells. TheTAG timing difference in FIG. 10 may be the difference in UE downlinkreception timing for downlink carriers in TAG1 and TAG2. The timingdifference may range between, for example, sub micro-seconds to about 30micro-seconds. Cells in TAG2 may use the same frame and subframe numbersof the cells in TAG1. Cells in TAG2 may use the same frame and subframenumbers of the pCell. Signals received in TAG1 and TAG2 are notsynchronized at OFDM symbol boundaries. Received signals of TAG1 may notbe employed for determining OFDM symbol boundaries of signals at TAG2.

FIG. 10 shows two different TAGs with two different downlink receptiontimings. In an example embodiment, a different type of grouping may beconfigured. For example, a downlink grouping may be configured whereincells with the same downlink timing are grouped in the same group.Instead of TAG1 and TAG2, a downlink group 1 and downlink group 2 may beconfigured, and cells in each downlink group may have a commonsynchronization process/mechanism.

FIG. 11 is a diagram depicting downlink reception timing of one or morecells. LAA Cell 1 and pCell may have the same received signal timing.There may be a timing difference between pCell and LAA cell 2 and LAAcell 3. For example, pCell and LAA cell 1 may be received from a firsttransmission point. LAA cell 2 and LAA cell 3 may be received from asecond transmission point.

In an example, LAA cell 2 and LAA cell 3 may be downlink only cells.Based on legacy principle LAA cell 2 and LAA cell 3 can only be groupedin a cell group including a cell with a configured uplink. For example,LAA cell 2 and LAA cell 3 may be grouped with pCell. Downlink receptiontiming of LAA cell 2 and LAA cell 3 is different from downlink receptiontiming of pCell, and LAA cell 2 and LAA cell 3 may not employ thedownlink signals received at the pCell for symbol level synchronization(e.g. fine synchronization). In an example embodiment, LAA cell 2 andLAA cell 3 may be grouped in an sTAG, even though both cells are DL onlycells. This is shown in FIG. 12, wherein pCell and LAA cell1 isconfigured in pTAG, and LAA Cell 2 and LAA Cell 3 are configured in ansTAG. LAA Cell 2 and LAA Cell 3 may be downlink only cells. In anotherexample, LAA Cell 2 and/or LAA Cell 3 may be configured with uplink.

FIG. 12 shows an example wherein LAA cell 2 and LAA cell 3 are twosynchronized cells transmitted from the same transmission point. LAAcell 2 and LAA cell 3 may be in the same band. In an example embodiment,DL only LAA cell 2 and DL only LAA cell 3 may be grouped in an sTAGdifferent from pTAG. LAA cell 2 and LAA cell 3 may be configured in aTAG without a cell with configured uplink. In an example embodiment, adifferent type of downlink grouping may be introduced for grouping LAAcell 2 and LAA cell 3 in a downlink synchronization group. FIG. 12 showsan example grouping, other example may be shown when a different numberof cells and a different number TAGs with a different configuration areimplemented.

FIG. 13 shows an example synchronization mechanism for unlicensed cells.The first signal may be, for example, synchronization signal, a type ofreference signal, and/or discovery signal. The first signal may be, forexample, DS signal used for downlink synchronization. The first signalmay be employed by the UE for downlink synchronization of the receivedsignal. The First signal may be an initial signal or burst signalincluding frame, subframe and/or symbol timing information. The firstsignal may be a downlink burst including timing information (e.g.initial signal, CRS, other types of RS, DRS, and/or other timinginformation). First signals transmitted by LAA cell 1 and LAA cell 2 maynot have the same configuration and/or format. In an example, Firstsignal 1 and First signal 4 transmitted on LAA Cell 1 may have differentformat or the same format. The First signal includes information aboutframe, subframe, and/or symbol timing. A UE may obtain synchronizationinformation from the received signal timing by processing the firstsignal. The timing information may be employed for coarsesynchronization and/or fine synchronization.

Due to LBT, LAA cells may not be able to transmit the first signal in agiven subframe, or a configured window of subframes. When the firstsignal is not transmitted, a UE may have difficulties in synchronizingitself with the received signal. In an example embodiment, a UE mayemploy the first signals transmitted on LAA cell 1 and LAA cell 2 tosynchronize itself with the received signal timing. FIG. 13 shows anexample. When a UE employs both first signals transmitted on LAA cell 1and LAA cell 2, the UE may receive and process more instances of thefirst signal for synchronization of both LAA cell 1 and LAA cell 2. Thismechanism may enhance the synchronization process and accuracy.

In an example embodiment, the first signal may be DS signal. DSconfiguration may be the same or different on LAA cell 1 and LAA cell 2.In an example, the first signal may be initial signal, CRS, and/ordownlink burst, or a combination of these signals. The first signal mayinclude synchronization signal. The first signal may include CSI-RSsignal. The first signal includes timing information of the downlinksignal. In an example, LAA cell1 and LAA cell2 may be DL only cellsbelonging to a TAG (or a different type of grouping). In an example, oneof or both of LAA cell 1 and LAA cell 2 may be configured with anuplink. FIG. 13 show two LAA cells, but the examples can be extendedwhen more than two LAA cells and one or more cells are configured. FIG.13 show two TAG groupings, but the examples may be extended when to adifferent type of grouping mechanism.

The join synchronization mechanism (e.g. in FIG. 13) may be implementedto enhance downlink synchronization. For example, the downlinksynchronization may be for measurement purposes, for example, RRM or CSImeasurements. The joint synchronization may be implemented forframe/subframe timing synchronization. The joint synchronization may beimplemented for coarse synchronization. The joint synchronization may beimplemented for symbol timing synchronization and/or finetuning/synchronization. In an example embodiment in FIG. 13, cell 1 mayemploy signals of cell 2, and cell 2 may employ signals of cell 1 fordownlink or uplink signal synchronization. In an example embodiment, thejoint synchronization may be employed for de-activated cells. In anexample embodiment, the joint synchronization may be employed foractivated cells. The accuracy of the synchronization may depend on theactivation status of the cells. Example embodiment may be implemented inone or both cases depending on the implementation requirements. In anexample, when an example embodiment is implemented for activated cells,timing signals received from inactivated cells may not be considered forjoint synchronization mechanism.

In an example embodiment, a wireless device may receive at least onecontrol message comprising configuration parameters of a plurality ofcells grouped into a plurality of cell groups. The plurality of cellgroups may comprise a first cell group and a second cell group. Thefirst cell group may comprise a first subset of the plurality of cells.Uplink transmission timing in the first cell group may be derivedemploying a first cell in the first cell group. The second cell groupmay comprise a first unlicensed cell and a second unlicensed cell in theplurality of cells. Uplink transmission timing in the second cell groupmay be derived employing at least a first signal received on the firstunlicensed cell and a second signal received on the second unlicensedcell.

In legacy systems, when UE is configured with an sTAG, the UE may use anactivated SCell from the sTAG (as a reference cell) for deriving the UEtransmit timing for cells in the sTAG. Selecting a specific unlicensedcell for deriving uplink synchronization may not be a reliable choice.Synchronization signals transmitted by an eNB on an unlicensed cell issubject to LBT. The UE may have to change its reference cell quitefrequently if the reference cell is an unlicensed cell. This may resultin timing jitters and synchronization errors, for example, when thereference cell is changed. In an enhanced mechanism, the UE may employthe signals of more than one cell as the reference signal. This mayreduce the probability of changing the reference cell and may improvethe synchronization mechanism. This may reduce the frequent change ofreference cell. Signals of two or more cells are employed fordetermining downlink reference synchronization signal and/or uplinktransmission timing. In an example embodiment, the two or more cells maybe required to be activated cells. Uplink signals may be transmitted onactivated cells. If the timing synchronization mechanism is employed fordeactivated status, the two or more cell may be activated ordeactivated.

FIG. 14 shows a configuration wherein at least one licensed cell and atleast one LAA cell are configured within the same group (e.g. a TAG). Inexample embodiments, signal transmission in cell 1 is not subject toLBT, but signal transmission in cell 2 is subject to LBT. The UE mayemploy synchronization and/or reference signals received on cell 1 tosynchronize itself with the signals received on LAA cell2. Cell1 andCell2 may be transmitted from the same transmission point. In an exampleembodiment, licensed cell 1 may be an activated cell.

In an example embodiment, limitations may be added to the reference cellselection mechanism in a TAG. In an example embodiment, when a TAGincludes one or more licensed cells and one or more unlicensed cells,the UE may choose an activated licensed cell as the timing reference (ifthere are any activated licensed cell in the cell group). In an exampleembodiment, a UE may use the PCell as the reference cell for driving theUE transmit timing for cells in the pTAG. A UE may be configured to usean activated licensed SCell from the sTAG (as a reference cell) forderiving the UE transmit timing for cells in the sTAG. A UE may not beallowed to choose an unlicensed cell as the timing reference if there isan activated licensed cell in the TAG. In an implementation, thelicensed cell is considered if it is activated. In an exampleimplementation, a UE may not use an activated unlicensed SCell from thesTAG (as a reference cell) for deriving the UE transmit timing for cellsin the sTAG (if there is an activated licensed cell in the TAG). In anexample transceiver, if synchronization employing de-activated cells isimplemented, a deactivated licensed cell may also provide timinginformation. This would require changes in existing secondary carriertransceiver design.

The mechanisms implemented in example embodiments may enhancesynchronization mechanism in a TAG including both licensed andunlicensed cells. Signal transmission in an unlicensed cell is subjectto LBT and the eNB may not be able to transmit synchronization signalsin the configured subframe or subframe window. In an example embodiment,a UE may receive a higher signal power from an unlicensed cell in agiven TAG compared with an activated unlicensed cell in the given TAG.The UE may not select the activated unlicensed cell as the referencecell (if there is an activated licensed cell in the group). This mayreduce the possibility of not receiving the synchronization signal dueto LBT. It may reduce the possibility of changing the reference cellfrequently as the air interface conditions (e.g. congestion,interference, signal level) in the LAA changes. When there is noactivated licensed cell in a TAG, then the UE may select one or moreunlicensed cell as the timing reference.

In an example embodiment, a wireless device may receive at least onecontrol message comprising configuration parameters of a plurality ofcells grouped into a plurality of cell groups. The plurality of cellgroups comprises a first cell group and a second cell group. The secondcell group may comprise one or more licensed cells and one or moreunlicensed cells. The wireless device may select a first cell in thesecond cell group as a reference cell according to a criterion. Thecriterion may comprise the first cell being a licensed cell. Thecriterion may further comprise the first cell being an activated cell.

In an example embodiment, if there is no activated licensed cell in thesecond cell group, the wireless device may use one or more unlicensedcells to obtain reference timing. The wireless device may transmituplink signals in the one or more licensed cells and the one or moreunlicensed cells. Transmission timing of the uplink signals is derivedemploying the first licensed cell as a timing reference cell (e.g. whenit is activated). When there are more than one activated licensed cellin the group, the wireless device may change the timing reference cellto a second cell. The second cell may be another activated licensed cellin the second cell group. The first cell group comprises a first subsetof the plurality of cells. Uplink transmission timing in the first cellgroup being derived employing a first licensed cell in the first cellgroup. The mechanisms in example embodiments may be implemented toachieve a better fine synchronization for activated cells.

In an example embodiment, depending on the accuracy of the requiredsynchronization (e.g. coarse synchronization) and/or whether thesynchronization is employed to in-activated cells, an inactivatedlicensed cell may provide reference timing information for other cellsin a group. The mechanisms in example embodiments may be implemented toachieve a better coarse synchronization for inactivated cells. Themechanisms in example embodiments may be implemented to achieve a bettercoarse synchronization. In an example embodiment, a deactivated licensedcell may provide coarse synchronization information for a deactivatedunlicensed cell. The timing information may be used, for example, forRRM measurement. For example, in FIG. 14, licensed cell 1 may providecoarse timing information for LAA cell 2 and LAA cell 1, when thelicense cell is deactivated.

In an example embodiment, when an sTAG includes LAA cells, a UE may notbe required to select a single LAA cell as the reference cell. Choosinga single licensed cell as the reference cell may result in frequentchanges in the reference cell in a given TAG. Uplink transmissions in aTAG including LAA cells may employ signals received on more than one LAAcell to achieve synchronization. When a UE is configured with an sTAGincluding two or more unlicensed cell, the UE may not rely only on oneactivated LAA Cell from the sTAG (as a reference cell) for deriving theUE transmit timing for cells in the sTAG. A UE may use more than onecell in the sTAG to drive downlink reception timing and/or uplinktransmission timing. If a TAG includes only one activated LAA cell, thenthat one activated LAA cell may be the reference for uplink transmissionin the TAG.

In an example embodiment, SCells and TAGs are configured employing RRCmessages. An eNB transmits one or more RRC messages to a UE to configurecells and TAGs. According to the current LTE-Advanced mechanism, sTAGconfiguration parameters include sTAG-Id and timeAlignmentTimerSTAG.STAG-ToAddMod-r11::=SEQUENCE {stag-Id-r11 STAG-Id-r11,timeAlignmentTimerSTAG-r11 TimeAlignmentTimer,}.TimeAlignmentTimer::=ENUMERATED {sf500, sf750, sf1280, sf1920, sf2560,sf5120, sf10240, infinity}.

The IE TimeAlignmentTimer is used to control how long the UE considersthe serving cells belonging to the associated TAG to be uplink timealigned. TimeAlignmentTimer may corresponds to the Timer for timealignment. In an example, TimeAlignmentTimer value is in number ofsub-frames. For example, value sf500 corresponds to 500 sub-frames,sf750 corresponds to 750 sub-frames and so on.

In an example embodiment, a TAG including only DL LAA cells may beconfigured. A TAG including DL only cells may not require aTimeAlignmentTimer. TimeAlignmentTimer may correspond to alignment ofuplink transmission timing. In an example embodiment, TimeAlignmentTimeris not configured, when an sTAG including DL only cells is configured.Time alignment timer may be set to infinity, or may be disabled/releasedfor an sTAG including DL only cells.

Transmission of timing signals in an LAA cell is subject to LBTrequirements. Timing signals may be for example synchronization signals,reference signals, discovery signals, initial signal and/or burstindicator signals. Timing signals are transmitted in the downlinkdirection. A wireless device may synchronize itself with the downlinksignals using the received timing information. Since the transmission oftiming signals in an LAA cell is subject to LBT requirements, an eNB maynot be able to receive timing signals (e.g. synch signals) for aconsiderable period of time. In an example scenario, the UE may lose itssynchronization and may need to restart the downlink synchronizationand/or search process. When a UE loses downlink synchronization it maynot be able to receive downlink signals intended for the UE in a givensubframe.

In an example embodiment, a timer is configured for a given cell group.The timer may indicate the synchronization status of a cell or a groupof cells. The cell or the group of cells may be considered out of synch,when the timer is expired. The cell or the group of cells may beconsidered in-synch when the timer is running. The timer for example maybe configured for an LAA cell or a cell group including one or more LAAcells. In an example, the timer may be applicable to a group of cellsincluding only LAA cells.

In an example embodiment one or more RRC message configuring a pluralityof cells and/or cell groups, may also comprise an IE for the value ofthe synchronization (or downlink alignment) timer. In an example, thevalue of downlink alignment timer may be configured for a cell, a cellgroup, or for a plurality of configured cells. The timer may be resetwhen eNB transmits a specific timing signal to the UE in a given cell orcell group.

In an example embodiment, downlink grouping may be informed using TAGconfiguration. For example, STAG-ToAddMod may comprise a downlink timealignment timer IE that may be used to control how long the UE considersthe serving cells belonging to the associated TAG to be downlink timealigned. Downlink time alignment timer may correspond to the timer fordownlink time alignment (e.g. downlink synchronization). An exampleconfiguration is shown here: STAG-ToAddMod-r11::=SEQUENCE {stag-Id-r11STAG-Id-r11, timeAlignmentTimerSTAG-r11 TimeAlignmentTimer,DLtimeAlignmentTimerSTAG TimeAlignmentTimer2}. In an example, instead ofa timer a counter may be employed, for example, counting the frames,subframes, etc.

In an example embodiment, a type of grouping different from TAG may beconfigured. Downlink timer/counter may be applicable to the group ofcells and indicate the status of downlink synchronization for the groupof cells. When the timer/counter expires the cells in the groups areconsidered downlink out of synch. The timer/counter of a cell or a groupof cells may be restarted when the eNB transmits a timing signal on thecell or a cell in the cell group. The cells may re-start downlinksynchronization, when the timer is expired. Downlink synchronization ina group of cells is performed jointly.

In an example embodiment, when downlink synchronization is expired, orfor any reason the wireless device loses downlink synchronization, thenboth downlink and uplink time alignment may be considered expired. Whena wireless device loses reference time of the downlink signals in a TAG,it may not be able to transmit uplink signals within the require timealignment. The UE may stop uplink transmissions to reduce unwantedinterference to other users. The timer/counter may be configured in eNBand/or in the UE.

In an example embodiment, downlink synchronization may not be used.Instead the eNB may detect that the UE is out of synch when it does notreceive a proper CSI feedback from the UE for the unlicensed cell. Forexample, when the eNB does not receive CSI feedback or when the eNBreceives out of range CSI feedback.

In an example embodiment, an eNB may maintain the timer and employ thestatus of the timer to determine whether the cell is in-sync orout-of-sync. In an example embodiment, a counter may be implemented formaintaining the downlink alignment/synchronization state. The countermay be incremented when a timing signal opportunity is missed (nottransmitted by eNB, or not received/decoded by the UE). When the timingsignal is received the counter may be reset. When the counter reaches apreconfigured value (for example, configured by an IE in an RRCmessage), the eNB and/or UE may consider that it is out of synch. Whenthe eNB and/or UE is considered out of synch, it may trigger certainactions. For example, deactivate/deconfigure/release the cell,transmit/receive a signal (e.g. RRC message, MAC/PHY signal) to informthe other node about the situation. In an example embodiment, thecounter may be implemented for a group of cells. A timing signaltransmitted on a cell in the group would reset the counter. The countermay determine the status of the synchronization signal for the group ofcells.

FIG. 15 is an example flow diagram as per an aspect of an embodiment ofthe present invention. The flow diagram may be processed as a method.The flow diagram may be executed by a wireless device. The wirelessdevice may comprise one or more processors and memory storinginstructions that, when executed, cause the wireless device to performactions described in the flow diagram.

The wireless device may receive at least one message at 1510. The atleast one message may comprise configuration parameters of a pluralityof cells. The plurality of cells may be grouped into a plurality oftiming advance groups (TAGs). The plurality of cells may comprise aplurality of downlink-uplink cells. Each of the plurality ofdownlink-uplink cells may have a configured uplink and a configureddownlink. The plurality of cells may comprise at least one downlink-onlycell. Each of the at least one downlink-only cell may have a configureddownlink with no configured uplink.

At 1520, the wireless device may receive a timing advance command (TAC)for a first TAG. The wireless device may apply the TAC to uplinktransmission timing in the first TAG at 1530. According to anembodiment, a TAG in the plurality of TAGs may be configurable toconsist of at least one downlink-only cell if the at least onedownlink-only cell is unlicensed. Otherwise, the TAG may comprise atleast one downlink-uplink cell in the plurality of downlink-uplinkcells.

According to an embodiment, the first TAG may comprise a first subset ofthe plurality of cells. Uplink transmission timing in the first TAG maybe derived employing a first cell in the first TAG. According to anembodiment, a time alignment timer of a second TAG may be disabled whenthe second TAG consists of one or more downlink-only cells. According toan embodiment, a time alignment timer may not be configured for a secondTAG when the second TAG consists of one or more downlink-only cells.According to an embodiment, at least one message may comprise a TAGindex. According to an embodiment, the TAC may comprise a TAG index anda timing advance value.

According to an embodiment, a TAG in the plurality of TAGs isconfigurable to consist of at least one downlink-only cell if thewireless device has a first capability, otherwise each TAG in theplurality of TAGs may comprise one or more downlink-uplink cells in theplurality of downlink-uplink cells. For example, the capability may besupporting configuration of unlicensed cells cell with certaincriterion, e.g. LAA cells with uplink and/or certain LTE releases,and/or certain configurations. According to an embodiment, theinstructions, when executed, may further cause the wireless device totransmit a second message comprising one or more parameters indicatingthe first capability to a base station. According to an embodiment, thefirst TAG may comprise a first subset of the plurality of cells and theuplink transmission timing in the first TAG may be derived employing afirst cell in the first TAG. According to an embodiment, a timealignment timer of a second TAG may be disabled when the second TAGconsists of one or more downlink-only cells. According to an embodiment,a time alignment timer may not be configured for a second TAG when thesecond TAG consists of one or more downlink-only cells. According to anembodiment, the at least one message may comprise a TAG index. Accordingto an embodiment, the TAC may comprise a TAG index and a timing advancevalue.

FIG. 16 is an example flow diagram as per an aspect of an embodiment ofthe present invention. The flow diagram may be processed as a method.The flow diagram may be executed by a base station. The base station maycomprise one or more processors and memory storing instructions that,when executed, cause the base station to perform actions described inthe flow diagram.

The base station may transmit at least one message to a wireless deviceat 1610. The message(s) may comprise configuration parameters of aplurality of cells grouped into a plurality of timing advance groups(TAGs). The plurality of cells may comprise a plurality ofdownlink-uplink cells, each of the plurality of downlink-uplink cellshaving a configured uplink and a configured downlink. The plurality ofcells may comprise at least one downlink-only cell. Each of thedownlink-only cell(s) may have a configured downlink with no configureduplink.

The base station may transmit a timing advance command (TAC) for a firstTAG at 1620. The base station may receive uplink signals on a cell inthe first TAG at 1630. A timing of uplink signals may depend, at leastin part, on the TAC.

A TAG in the plurality of TAGs may be configurable to consist of atleast one downlink-only cell if the wireless device has a firstcapability. Otherwise, each TAG in the plurality of TAGs may comprise atleast one downlink-uplink cells in the plurality of downlink-uplinkcells. According to an embodiment, the instructions, when executed, mayfurther cause the base station to receive a second message from thewireless device. The second message may comprise one or more parametersindicating the first capability. For example, the first capability maybe supporting configuration of unlicensed cells cell with certaincriterion, e.g. LAA cells with uplink and/or certain LTE releases,and/or certain configurations. According to an embodiment, the first TAGmay comprise a first subset of the plurality of cells, uplinktransmission timing in the first TAG derived employing a first cell inthe first TAG. According to an embodiment, a time alignment timer of asecond TAG may be disabled when the second TAG consists of one or moredownlink-only cells. According to an embodiment, a time alignment timermay not be configured for a second TAG when the second TAG consists ofone or more downlink-only cells. According to an embodiment, the atleast one message may comprise a TAG index. According to an embodiment,the TAC may comprise a TAG index and a timing advance value.

FIG. 17 is an example flow diagram as per an aspect of an embodiment ofthe present invention. The flow diagram may be processed as a method.The flow diagram may be executed by a wireless device. The wirelessdevice may comprise one or more processors and memory storinginstructions that, when executed, cause the wireless device to performactions described in the flow diagram.

At 1710, the wireless device may receive at least one control message.The control message(s) may comprise configuration parameters of aplurality of cells. The cell(s) may comprise two or more unlicensedcells comprising a first unlicensed cell and a second unlicensed cell.At 1720, the wireless device may synchronize the reception timing of thefirst unlicensed cell employing at least a second received signal of thesecond unlicensed cell.

According to an embodiment, the instructions, when executed, may furthercause the wireless device to synchronize reception timing of the secondunlicensed cell employing at least a first received signal of the firstunlicensed licensed cell. According to an embodiment, the secondreceived signal may comprise a synchronization signal. According to anembodiment, the second received signal may comprise a discovery signal,a reference signal, and/or the like.

According to an embodiment, the plurality of cells may be grouped into aplurality of cell groups. The plurality of cell groups may comprise afirst cell group comprising a first subset of the plurality of cellswhere the uplink transmission timing in the first cell group may bederived employing a first cell in the first cell group. The plurality ofcell groups may comprise a second cell group comprising the firstunlicensed cell and the second unlicensed cell.

According to an embodiment, the control message(s) may configure a cellgroup comprising the first unlicensed cell and the second unlicensedcell. According to an embodiment, a cell group may be configured atleast for downlink synchronization. According to an embodiment, at leastone of the two or more unlicensed cells may be a licensed assistedaccess (LAA) cell. According to an embodiment, a transmission of thesecond received signal may be subject to a listen before talk (LBT)mechanism.

FIG. 18 is an example flow diagram as per an aspect of an embodiment ofthe present invention. The flow diagram may be processed as a method.The flow diagram may be executed by a wireless device. The wirelessdevice may comprise one or more processors and memory storinginstructions that, when executed, cause the wireless device to performactions described in the flow diagram.

A wireless device may receive control message(s) at 1810. The controlmessage(s) may comprising configuration parameters of a plurality ofcells. The plurality of cells may be grouped into a plurality of timingadvance groups (TAGs). The TAGs may comprise a first TAG.

A first cell in the first TAG may be selected according to a criterionat 1820. The TAG may comprise one or more licensed cells and one or moreunlicensed cells. The criterion may comprise the first cell beinglicensed. According to an embodiment, the criterion may further comprisethe first cell being an activated cell. According to an embodiment, thecriterion may further comprise the first cell meeting signal qualitycriteria, e.g. having a signal level and/or signal quality indication,and/or other signal qualities meeting a threshold. According to anembodiment, the criterion may further comprise selecting an unlicensedcell in a first TAG as a first timing reference cell when the first TAGdoes not comprise a cell that is licensed. According to an embodiment,the criterion may further comprise selecting an unlicensed cell in afirst TAG as a first timing reference cell when the first TAG does notcomprise a cell that is licensed and activated.

Uplink signals in the first TAG may be transmitted at 1830. Thetransmission timing of the uplink signals may be derived employing thefirst cell as a timing reference cell. According to an embodiment, thewireless device may further comprise changing the timing reference cellto a second cell. The second cell may be an activated licensed cell in asecond cell group. According to an embodiment, the uplink signals may betransmitted on at least one of the licensed cell(s) and at least one ofthe unlicensed cell(s). According to an embodiment, an unlicensed cellmay be a licensed assisted access (LAA) cell. According to anembodiment, the wireless device may further comprise receiving a timingadvance command comprising a TAG index and a timing advance value.According to an embodiment, the wireless device may apply the timingadvance value to uplink transmission timing of a first TAG identified bythe TAG index. According to an embodiment, the at least one messagecomprises a time alignment timer for the first TAG.

FIG. 19 is an example flow diagram as per an aspect of an embodiment ofthe present invention. The flow diagram may be processed as a method.The flow diagram may be executed by a wireless device. The wirelessdevice may comprise one or more processors and memory storinginstructions that, when executed, cause the wireless device to performactions described in the flow diagram.

A wireless device may receive control message(s) at 1910. The controlmessage(s) may comprising configuration parameters of a plurality ofcells. The plurality of cells may be grouped into a plurality of timingadvance groups (TAGs). The TAGs may comprise a first TAG and a secondTAG. The first TAG may comprise a first subset of the plurality ofcells. Uplink transmission timing in the first TAG may be derivedemploying a first cell in the first TAG. The second TAG may comprise afirst unlicensed cell and a second unlicensed cell. Uplink transmissiontiming in the second TAG may be derived employing at least: a firstsignal received on the first unlicensed cell; and a second signalreceived on the second unlicensed cell.

A timing advance command (TAC) received at 1920. The TAC may comprise atime adjustment value and a TAG index. The TAC may be applied to theuplink transmission timing at 1930 in one of the first TAG or the secondTAG that corresponds to the TAG index.

According to an embodiment, an unlicensed cell may be a licensedassisted access (LAA) cell. According to an embodiment, the second TAGmay not comprise an activated licensed cell. According to an embodiment,the message(s) may comprise the TAG index. According to an embodiment,the message(s) may comprises a time alignment timer for the TAG.According to an embodiment, the first TAG may comprise an unlicensedcell.

According to an embodiment, the first signal may comprise at least oneof the following: a synchronization signal, a discovery signal, or areference signal. According to an embodiment, the second signal maycomprise at least one of the following: a synchronization signal, adiscovery signal, or a reference signal. According to an embodiment, atransmission of the first signal or the second signal may be subject toa listen before talk (LBT) mechanism. According to an embodiment, thewireless device may further comprise selecting a second cell in thefirst TAG as a timing reference when a first criterion is met. Thesecond uplink transmission timing in the first TAG may be derivedemploying the second cell.

In this specification, “a” and “an” and similar phrases are to beinterpreted as “at least one” and “one or more.” In this specification,the term “may” is to be interpreted as “may, for example.” In otherwords, the term “may” is indicative that the phrase following the term“may” is an example of one of a multitude of suitable possibilities thatmay, or may not, be employed to one or more of the various embodiments.If A and B are sets and every element of A is also an element of B, A iscalled a subset of B. In this specification, only non-empty sets andsubsets are considered. For example, possible subsets of B={cell1,cell2} are: {cell1}, {cell2}, and {cell1, cell2}.

In this specification, parameters (Information elements: IEs) maycomprise one or more objects, and each of those objects may comprise oneor more other objects. For example, if parameter (IE) N comprisesparameter (IE) M, and parameter (IE) M comprises parameter (IE) K, andparameter (IE) K comprises parameter (information element) J, then, forexample, N comprises K, and N comprises J. In an example embodiment,when one or more messages comprise a plurality of parameters, it impliesthat a parameter in the plurality of parameters is in at least one ofthe one or more messages, but does not have to be in each of the one ormore messages.

Many of the elements described in the disclosed embodiments may beimplemented as modules. A module is defined here as an isolatableelement that performs a defined function and has a defined interface toother elements. The modules described in this disclosure may beimplemented in hardware, software in combination with hardware,firmware, wetware (i.e. hardware with a biological element) or acombination thereof, all of which are behaviorally equivalent. Forexample, modules may be implemented as a software routine written in acomputer language configured to be executed by a hardware machine (suchas C, C++, Fortran™, Java™, Basic, Matlab™ or the like) or amodeling/simulation program such as Simulink™, Stateflow™, GNU Octave™,or LabVIEWMathScript™. Additionally, it may be possible to implementmodules using physical hardware that incorporates discrete orprogrammable analog, digital and/or quantum hardware. Examples ofprogrammable hardware comprise: computers, microcontrollers,microprocessors, application-specific integrated circuits (ASICs); fieldprogrammable gate arrays (FPGAs); and complex programmable logic devices(CPLDs). Computers, microcontrollers and microprocessors are programmedusing languages such as assembly, C, C++ or the like. FPGAs, ASICs andCPLDs are often programmed using hardware description languages (HDL)such as VHSIC hardware description language (VHDL) or Verilog thatconfigure connections between internal hardware modules with lesserfunctionality on a programmable device. Finally, it needs to beemphasized that the above mentioned technologies are often used incombination to achieve the result of a functional module.

The disclosure of this patent document incorporates material which issubject to copyright protection. The copyright owner has no objection tothe facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the Patent and Trademark Officepatent file or records, for the limited purposes required by law, butotherwise reserves all copyright rights whatsoever.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevantart(s) that various changes in form and detail can be made thereinwithout departing from the spirit and scope. In fact, after reading theabove description, it will be apparent to one skilled in the relevantart(s) how to implement alternative embodiments. Thus, the presentembodiments should not be limited by any of the above describedexemplary embodiments. In particular, it should be noted that, forexample purposes, the above explanation has focused on the example(s)using FDD communication systems. However, one skilled in the art willrecognize that embodiments of the invention may also be implemented in asystem comprising one or more TDD cells (e.g. frame structure 2 and/orframe structure 3-licensed assisted access). The disclosed methods andsystems may be implemented in wireless or wireline systems. The featuresof various embodiments presented in this invention may be combined. Oneor many features (method or system) of one embodiment may be implementedin other embodiments. Only a limited number of example combinations areshown to indicate to one skilled in the art the possibility of featuresthat may be combined in various embodiments to create enhancedtransmission and reception systems and methods.

In addition, it should be understood that any figures which highlightthe functionality and advantages, are presented for example purposesonly. The disclosed architecture is sufficiently flexible andconfigurable, such that it may be utilized in ways other than thatshown. For example, the actions listed in any flowchart may bere-ordered or only optionally used in some embodiments.

Further, the purpose of the Abstract of the Disclosure is to enable theU.S. Patent and Trademark Office and the public generally, andespecially the scientists, engineers and practitioners in the art whoare not familiar with patent or legal terms or phraseology, to determinequickly from a cursory inspection the nature and essence of thetechnical disclosure of the application. The Abstract of the Disclosureis not intended to be limiting as to the scope in any way.

Finally, it is the applicant's intent that only claims that include theexpress language “means for” or “step for” be interpreted under 35U.S.C. 112, paragraph 6. Claims that do not expressly include the phrase“means for” or “step for” are not to be interpreted under 35 U.S.C. 112.

What is claimed is:
 1. A wireless device comprising: one or moreprocessors; and memory storing instructions that, when executed by theone or more processors, cause the wireless device to: receiveconfiguration parameters of a first unlicensed cell and a secondunlicensed cell; receive, via the first unlicensed cell, a first signalcomprising a first downlink synchronization signal; receive, via thesecond unlicensed cell, a second signal comprising a second downlinksynchronization signal; synchronize a first downlink signal timing withthe first unlicensed cell based on the second signal received via thesecond unlicensed cell; and synchronize a second downlink signal timingwith the second unlicensed cell based on the first signal received viathe first unlicensed cell.
 2. The wireless device of claim 1, whereinthe first signal is received in a plurality of subframes.
 3. Thewireless device of claim 1, wherein the second signal is received in aplurality of subframes.
 4. The wireless device of claim 1, wherein thesecond signal comprises a discovery signal.
 5. The wireless device ofclaim 1, wherein the second signal comprises a reference signal.
 6. Thewireless device of claim 1, wherein the configuration parametersconfigure a secondary cell group comprising the first unlicensed celland the second unlicensed cell.
 7. The wireless device of claim 1,wherein a cell group is configured at least for downlinksynchronization.
 8. The wireless device of claim 1, wherein at least oneof the first unlicensed cell and the second unlicensed cell is alicensed assisted access cell.
 9. The wireless device of claim 1,wherein a transmission of the second signal is subject to a listenbefore talk mechanism.
 10. A method comprising: receiving, by a wirelessdevice, configuration parameters of a first unlicensed cell and a secondunlicensed cell; receiving, via the first unlicensed cell, a firstsignal comprising a first downlink synchronization signal; receiving,via the second unlicensed cell, a second signal comprising a seconddownlink synchronization signal; synchronizing a first downlink signaltiming with the first unlicensed cell based on the second signalreceived via the second unlicensed cell; and synchronizing a seconddownlink signal timing with the second unlicensed cell based on thefirst signal received via the first unlicensed cell.
 11. The method ofclaim 10, wherein the first signal is received in a plurality ofsubframes.
 12. The method of claim 10, wherein the second signal isreceived in a plurality of subframes.
 13. The method of claim 10,wherein the second signal comprises a discovery signal.
 14. The methodof claim 10, wherein the second signal comprises a reference signal. 15.The method of claim 10, wherein the configuration parameters configure asecondary cell group comprising the first unlicensed cell and the secondunlicensed cell.
 16. The method of claim 10, wherein a cell group isconfigured at least for downlink synchronization.
 17. The method ofclaim 10, wherein at least one of the first unlicensed cell and thesecond unlicensed cell is a licensed assisted access cell.
 18. Themethod of claim 10, wherein a transmission of the second signal issubject to a listen before talk mechanism.